diff --git a/packages/ketcher-core/src/application/editor/editor.types.ts b/packages/ketcher-core/src/application/editor/editor.types.ts
index 4e0726c37e..ba0c47de02 100644
--- a/packages/ketcher-core/src/application/editor/editor.types.ts
+++ b/packages/ketcher-core/src/application/editor/editor.types.ts
@@ -41,6 +41,7 @@ export interface Editor {
   isDitrty: () => boolean
   setOrigin: () => void
   struct: (struct?: Struct) => Struct
+  structToAddFragment: (struct: Struct) => Struct
   subscribe: (eventName: string, handler: (data?: any) => any) => any
   unsubscribe: (eventName: string, subscriber: any) => void
   selection: (arg?: Selection | 'all' | null) => Selection | null
diff --git a/packages/ketcher-core/src/application/ketcher.ts b/packages/ketcher-core/src/application/ketcher.ts
index d7d4592cbc..2c3b2b560f 100644
--- a/packages/ketcher-core/src/application/ketcher.ts
+++ b/packages/ketcher-core/src/application/ketcher.ts
@@ -27,6 +27,19 @@ import { MolfileFormat } from 'domain/serializers'
 import { Struct } from 'domain/entities'
 import assert from 'assert'
 
+async function prepareStructToRender(
+  structStr: string,
+  structService: StructService
+): Promise<Struct> {
+  const struct: Struct = await parseStruct(structStr, structService)
+  struct.initHalfBonds()
+  struct.initNeighbors()
+  struct.setImplicitHydrogen()
+  struct.markFragments()
+
+  return struct
+}
+
 function parseStruct(structStr: string, structService: StructService) {
   const format = identifyStructFormat(structStr)
   const factory = new FormatterFactory(structService)
@@ -150,18 +163,23 @@ export class Ketcher {
   async setMolecule(structStr: string): Promise<void> {
     assert(typeof structStr === 'string')
 
-    const struct: Struct = await parseStruct(structStr, this.#structService)
-    struct.initHalfBonds()
-    struct.initNeighbors()
-    struct.setImplicitHydrogen()
-    struct.markFragments()
+    const struct: Struct = await prepareStructToRender(
+      structStr,
+      this.#structService
+    )
+
     this.#editor.struct(struct)
   }
 
-  async addFragment(fragment: string): Promise<void> {
-    assert(typeof fragment === 'string')
+  async addFragment(structStr: string): Promise<void> {
+    assert(typeof structStr === 'string')
+
+    const struct: Struct = await prepareStructToRender(
+      structStr,
+      this.#structService
+    )
 
-    throw Error('not implemented yet')
+    this.#editor.structToAddFragment(struct)
   }
 
   recognize(image: Blob, version?: string): Promise<Struct> {
diff --git a/packages/ketcher-react/src/script/editor/Editor.ts b/packages/ketcher-react/src/script/editor/Editor.ts
index 093315d067..4c6b1b945b 100644
--- a/packages/ketcher-react/src/script/editor/Editor.ts
+++ b/packages/ketcher-react/src/script/editor/Editor.ts
@@ -99,6 +99,7 @@ interface Selection {
   rxnPluses?: Array<number>
   rxnArrows?: Array<number>
 }
+
 class Editor implements KetcherEditor {
   #origin?: any
   render: Render
@@ -146,6 +147,8 @@ class Editor implements KetcherEditor {
     this.historyPtr = 0
     this.errorHandler = null
     this.highlights = new Highlighter(this)
+    this.renderAndRecoordinateStruct =
+      this.renderAndRecoordinateStruct.bind(this)
 
     this.event = {
       message: new Subscription(),
@@ -209,6 +212,15 @@ class Editor implements KetcherEditor {
     this.struct(undefined)
   }
 
+  renderAndRecoordinateStruct(struct: Struct) {
+    const action = fromNewCanvas(this.render.ctab, struct)
+    this.update(action)
+
+    const structCenter = getStructCenter(this.render.ctab)
+    recoordinate(this, structCenter)
+    return this.render.ctab.molecule
+  }
+
   struct(value?: Struct): Struct {
     if (arguments.length === 0) {
       return this.render.ctab.molecule
@@ -216,12 +228,15 @@ class Editor implements KetcherEditor {
 
     this.selection(null)
     const struct = value || new Struct()
-    const action = fromNewCanvas(this.render.ctab, struct)
-    this.update(action)
 
-    const structCenter = getStructCenter(this.render.ctab)
-    recoordinate(this, structCenter)
-    return this.render.ctab.molecule
+    return this.renderAndRecoordinateStruct(struct)
+  }
+
+  // this is used by API addFragment method
+  structToAddFragment(value: Struct): Struct {
+    const superStruct = value.mergeInto(this.render.ctab.molecule)
+
+    return this.renderAndRecoordinateStruct(superStruct)
   }
 
   options(value?: any) {