diff --git a/packages/core/src/components/fields/ObjectField.tsx b/packages/core/src/components/fields/ObjectField.tsx
index 107cda80df..dfde7fe1c3 100644
--- a/packages/core/src/components/fields/ObjectField.tsx
+++ b/packages/core/src/components/fields/ObjectField.tsx
@@ -202,13 +202,16 @@ class ObjectField<T = any, S extends StrictRJSFSchema = RJSFSchema, F extends Fo
     const newFormData = { ...formData } as T;
 
     let type: RJSFSchema['type'] = undefined;
+    let defaultValue: RJSFSchema['default'] = undefined;
     if (isObject(schema.additionalProperties)) {
       type = schema.additionalProperties.type;
+      defaultValue = schema.additionalProperties.default;
       let apSchema = schema.additionalProperties;
       if (REF_KEY in apSchema) {
         const { schemaUtils } = registry;
         apSchema = schemaUtils.retrieveSchema({ $ref: apSchema[REF_KEY] } as S, formData);
         type = apSchema.type;
+        defaultValue = apSchema.default;
       }
       if (!type && (ANY_OF_KEY in apSchema || ONE_OF_KEY in apSchema)) {
         type = 'object';
@@ -217,7 +220,7 @@ class ObjectField<T = any, S extends StrictRJSFSchema = RJSFSchema, F extends Fo
 
     const newKey = this.getAvailableKey('newKey', newFormData);
     // Cast this to make the `set` work properly
-    set(newFormData as GenericObjectType, newKey, this.getDefaultValue(type));
+    set(newFormData as GenericObjectType, newKey, defaultValue ?? this.getDefaultValue(type));
 
     onChange(newFormData);
   };
diff --git a/packages/core/test/ObjectField.test.jsx b/packages/core/test/ObjectField.test.jsx
index 2f905a4010..1f0c2d2cf7 100644
--- a/packages/core/test/ObjectField.test.jsx
+++ b/packages/core/test/ObjectField.test.jsx
@@ -896,6 +896,50 @@ describe('ObjectField', () => {
       });
     });
 
+    it("should add a new default item if default is provided in the additionalProperties' schema", () => {
+      const customSchema = {
+        ...schema,
+        additionalProperties: {
+          type: 'string',
+          default: 'default value',
+        },
+      };
+      const { node, onChange } = createFormComponent({
+        schema: customSchema,
+        formData: {},
+      });
+
+      fireEvent.click(node.querySelector('.object-property-expand button'));
+
+      sinon.assert.calledWithMatch(onChange.lastCall, {
+        formData: {
+          newKey: 'default value',
+        },
+      });
+    });
+
+    it('should add a new default item even if the schema of default value is invalid', () => {
+      const customSchema = {
+        ...schema,
+        additionalProperties: {
+          type: 'string',
+          default: 1,
+        },
+      };
+      const { node, onChange } = createFormComponent({
+        schema: customSchema,
+        formData: {},
+      });
+
+      fireEvent.click(node.querySelector('.object-property-expand button'));
+
+      sinon.assert.calledWithMatch(onChange.lastCall, {
+        formData: {
+          newKey: 1,
+        },
+      });
+    });
+
     it('should not provide an expand button if length equals maxProperties', () => {
       const { node } = createFormComponent({
         schema: { maxProperties: 1, ...schema },