diff --git a/frontend/src/components/Simulator/ContractParams.vue b/frontend/src/components/Simulator/ContractParams.vue
index ee37771b2..a4c122235 100644
--- a/frontend/src/components/Simulator/ContractParams.vue
+++ b/frontend/src/components/Simulator/ContractParams.vue
@@ -105,6 +105,7 @@ onMounted(() => {
         :name="paramName"
         :placeholder="`${paramType}`"
         :label="paramName"
+        :unionTypes="inputMap.getUnionTypes(paramType)"
       />
     </div>
     <div
@@ -119,6 +120,7 @@ onMounted(() => {
         :name="paramName"
         :placeholder="`${paramType}`"
         :label="paramName"
+        :unionTypes="inputMap.getUnionTypes(paramType)"
       />
     </div>
   </div>
diff --git a/frontend/src/components/global/fields/UnionField.vue b/frontend/src/components/global/fields/UnionField.vue
new file mode 100644
index 000000000..6aa907a15
--- /dev/null
+++ b/frontend/src/components/global/fields/UnionField.vue
@@ -0,0 +1,256 @@
+<script setup lang="ts">
+import { ref, watch, computed } from 'vue';
+import { useUniqueId } from '@/hooks';
+import TextInput from '../inputs/TextInput.vue';
+import NumberInput from '../inputs/NumberInput.vue';
+import CheckboxInput from '../inputs/CheckboxInput.vue';
+import FieldLabel from './FieldLabel.vue';
+import { AnyFieldValue } from './AnyFieldValue';
+
+const props = defineProps<{
+  name: string;
+  unionTypes: string[];
+  modelValue?: any;
+}>();
+
+const emit = defineEmits<{
+  'update:modelValue': [value: any];
+}>();
+
+const fieldId = useUniqueId('union');
+const selectedType = ref<string>('');
+const selectedGroup = ref<string>('');
+const values = ref<{ [key: string]: any }>({});
+const isInternalUpdate = ref<boolean>(false);
+
+const getInputComponent = (type: string) => {
+  switch (type) {
+    case 'int':
+      return NumberInput;
+    case 'bool':
+      return CheckboxInput;
+    default:
+      return TextInput;
+  }
+};
+
+const displayGroups = computed(() => {
+  const groups: {
+    id: string;
+    types: string[];
+    label: string;
+    placeholder: string;
+  }[] = [];
+  const processed = new Set<string>();
+
+  props.unionTypes.forEach((type) => {
+    const trimmedType = type.trim();
+    if (processed.has(trimmedType)) return;
+
+    const component = getInputComponent(trimmedType);
+
+    if (
+      component === TextInput &&
+      ['array', 'dict', 'address', 'bytes', 'any'].includes(trimmedType)
+    ) {
+      const complexTypes = props.unionTypes.filter((t) => {
+        const tt = t.trim();
+        return ['array', 'dict', 'address', 'bytes', 'any'].includes(tt);
+      });
+
+      if (complexTypes.length > 0) {
+        const typeLabels = complexTypes.map((t) => t.trim().toLowerCase());
+        groups.push({
+          id: 'complex',
+          types: complexTypes.map((t) => t.trim()),
+          label: typeLabels.join(','),
+          placeholder: typeLabels.join('/'),
+        });
+
+        complexTypes.forEach((t) => processed.add(t.trim()));
+      }
+    } else if (!processed.has(trimmedType)) {
+      groups.push({
+        id: trimmedType,
+        types: [trimmedType],
+        label: trimmedType,
+        placeholder: trimmedType.toLowerCase(),
+      });
+      processed.add(trimmedType);
+    }
+  });
+
+  return groups;
+});
+
+const initializeValues = () => {
+  if (!props.unionTypes || props.unionTypes.length === 0) {
+    return;
+  }
+  const typeMap: { [key: string]: any } = {
+    string: '',
+    int: 0,
+    bool: false,
+    address: '',
+    bytes: '',
+    array: '',
+    dict: '',
+    None: null,
+    null: null,
+    any: '',
+  };
+
+  props.unionTypes.forEach((type) => {
+    const trimmedType = type.trim();
+    if (!trimmedType) return;
+    // Only initialize if the value doesn't already exist (preserve user input)
+    if (!(trimmedType in values.value)) {
+      values.value[trimmedType] = typeMap[trimmedType] ?? '';
+    }
+  });
+
+  const groups = displayGroups.value;
+  if (groups.length > 0) {
+    selectedGroup.value = groups[0].id;
+    selectedType.value = groups[0].types[0];
+  } else {
+    console.warn('No valid union type groups found');
+  }
+};
+
+// Handle external model value updates
+watch(
+  () => props.modelValue,
+  (newValue) => {
+    // Skip if this update is from our own emitValue
+    if (isInternalUpdate.value) {
+      isInternalUpdate.value = false;
+      return;
+    }
+
+    // Skip if the new value matches what we already have for the current type
+    // This prevents overwriting user input when switching radio buttons
+    if (newValue !== undefined && newValue instanceof AnyFieldValue) {
+      const currentValue = values.value[selectedType.value];
+      if (typeof currentValue === 'string' && currentValue === newValue.value) {
+        return;
+      }
+    }
+
+    if (newValue !== undefined && newValue instanceof AnyFieldValue) {
+      // For strings, unwrap the JSON to get the original value
+      if (typeof newValue.value === 'string') {
+        try {
+          values.value[selectedType.value] = JSON.parse(newValue.value);
+        } catch {
+          values.value[selectedType.value] = newValue.value;
+        }
+      } else {
+        values.value[selectedType.value] = newValue.value;
+      }
+    }
+  },
+);
+
+const getCurrentValue = () => {
+  const type = selectedType.value;
+  const value = values.value[type];
+
+  if (!type || value === undefined) {
+    return undefined;
+  }
+
+  if (type === 'string') {
+    return new AnyFieldValue(JSON.stringify(value));
+  }
+
+  if (
+    type === 'array' ||
+    type === 'dict' ||
+    type === 'address' ||
+    type === 'bytes' ||
+    type === 'any'
+  ) {
+    return new AnyFieldValue(value);
+  }
+
+  return value;
+};
+
+const emitValue = () => {
+  const currentValue = getCurrentValue();
+  isInternalUpdate.value = true;
+  emit('update:modelValue', currentValue);
+};
+
+// Initialize and watch for changes
+watch(
+  () => props.unionTypes,
+  (newTypes) => {
+    if (newTypes?.length > 0) {
+      initializeValues();
+      emitValue();
+    }
+  },
+  { immediate: true },
+);
+
+// Watch for group changes to update selected type
+watch(selectedGroup, (newGroup) => {
+  const groups = displayGroups.value;
+  const group = groups.find((g) => g.id === newGroup);
+  if (group && group.types.length > 0) {
+    selectedType.value = group.types[0];
+    emitValue();
+  }
+});
+
+// Watch for value changes
+watch([selectedType, values], () => {
+  emitValue();
+});
+</script>
+
+<template>
+  <div class="flex w-full flex-col gap-2">
+    <FieldLabel :for="fieldId" tiny>{{ name }}</FieldLabel>
+
+    <div class="flex flex-col gap-2">
+      <div
+        v-for="group in displayGroups"
+        :key="group.id"
+        class="flex w-full flex-row items-center gap-2"
+      >
+        <input
+          :id="`${fieldId}-radio-${group.id}`"
+          v-model="selectedGroup"
+          :value="group.id"
+          type="radio"
+          :name="`${fieldId}-group`"
+          class="text-primary-600 h-4 w-4 border-gray-300 text-primary outline-0 focus:ring-accent dark:border-gray-500 dark:bg-transparent dark:text-accent"
+        />
+
+        <div
+          v-if="group.id === 'None' || group.id === 'null'"
+          class="text-xs text-gray-500"
+        >
+          None
+        </div>
+
+        <div v-else class="flex w-full flex-row items-center gap-2">
+          <component
+            :is="getInputComponent(group.types[0])"
+            v-model="values[group.types[0]]"
+            :placeholder="group.placeholder"
+            :disabled="selectedGroup !== group.id"
+            :id="`${fieldId}-${group.id}`"
+            :name="`${props.name}-${group.id}`"
+            @update:modelValue="emitValue"
+            tiny
+            :class="group.types[0] === 'bool' ? 'h-4 w-4' : 'w-full flex-1'"
+          />
+        </div>
+      </div>
+    </div>
+  </div>
+</template>
diff --git a/frontend/src/hooks/useInputMap.ts b/frontend/src/hooks/useInputMap.ts
index 8e1b6928c..5c7a88237 100644
--- a/frontend/src/hooks/useInputMap.ts
+++ b/frontend/src/hooks/useInputMap.ts
@@ -2,6 +2,7 @@ import AnyField from '@/components/global/fields/AnyField.vue';
 import StringField from '@/components/global/fields/StringField.vue';
 import IntegerField from '@/components/global/fields/IntegerField.vue';
 import BooleanField from '@/components/global/fields/BooleanField.vue';
+import UnionField from '@/components/global/fields/UnionField.vue';
 import type { ContractParamsSchema } from 'genlayer-js/types';
 
 export const InputTypesMap: { [k: string]: any } = {
@@ -13,9 +14,14 @@ export const InputTypesMap: { [k: string]: any } = {
 
 export const useInputMap = () => {
   const getComponent = (type: ContractParamsSchema) => {
+    if (typeof type === 'object' && type !== null && '$or' in type) {
+      return UnionField;
+    }
+
     if (typeof type !== 'string') {
       type = 'any';
     }
+
     const component = InputTypesMap[type];
 
     if (!component) {
@@ -28,5 +34,13 @@ export const useInputMap = () => {
     return component;
   };
 
-  return { getComponent };
+  const getUnionTypes = (type: ContractParamsSchema): string[] => {
+    if (typeof type === 'object' && type !== null && '$or' in type) {
+      return (type as any).$or || [];
+    }
+
+    return [];
+  };
+
+  return { getComponent, getUnionTypes };
 };