diff --git a/api/errors/errors.go b/api/errors/errors.go
index ae548d33..33ec96e3 100644
--- a/api/errors/errors.go
+++ b/api/errors/errors.go
@@ -73,6 +73,7 @@ const (
 	ErrInvalidArgument
 	ErrInvalidTagKey
 	ErrInvalidTagValue
+	ErrInvalidTagKeyUniqueness
 	ErrInvalidTagsSizeExceed
 	ErrNotImplemented
 	ErrPreconditionFailed
@@ -526,13 +527,19 @@ var errorCodes = errorCodeMap{
 	ErrInvalidTagKey: {
 		ErrCode:        ErrInvalidTagKey,
 		Code:           "InvalidTag",
-		Description:    "The TagValue you have provided is invalid",
+		Description:    "The TagKey you have provided is invalid",
 		HTTPStatusCode: http.StatusBadRequest,
 	},
 	ErrInvalidTagValue: {
 		ErrCode:        ErrInvalidTagValue,
 		Code:           "InvalidTag",
-		Description:    "The TagKey you have provided is invalid",
+		Description:    "The TagValue you have provided is invalid",
+		HTTPStatusCode: http.StatusBadRequest,
+	},
+	ErrInvalidTagKeyUniqueness: {
+		ErrCode:        ErrInvalidTagKeyUniqueness,
+		Code:           "InvalidTag",
+		Description:    "Cannot provide multiple Tags with the same key",
 		HTTPStatusCode: http.StatusBadRequest,
 	},
 	ErrInvalidTagsSizeExceed: {
diff --git a/api/handler/tagging.go b/api/handler/tagging.go
index bd56451d..10258036 100644
--- a/api/handler/tagging.go
+++ b/api/handler/tagging.go
@@ -219,6 +219,9 @@ func (h *handler) readTagSet(reader io.Reader) (map[string]string, error) {
 
 	tagSet := make(map[string]string, len(tagging.TagSet))
 	for _, tag := range tagging.TagSet {
+		if _, ok := tagSet[tag.Key]; ok {
+			return nil, errors.GetAPIError(errors.ErrInvalidTagKeyUniqueness)
+		}
 		tagSet[tag.Key] = tag.Value
 	}
 
diff --git a/api/handler/tagging_test.go b/api/handler/tagging_test.go
index 98b39a79..27ef7be3 100644
--- a/api/handler/tagging_test.go
+++ b/api/handler/tagging_test.go
@@ -1,9 +1,11 @@
 package handler
 
 import (
+	"net/http"
 	"strings"
 	"testing"
 
+	apiErrors "git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/errors"
 	"github.com/stretchr/testify/require"
 )
 
@@ -44,3 +46,66 @@ func TestTagsValidity(t *testing.T) {
 		}
 	}
 }
+
+func TestPutObjectTaggingCheckUniqueness(t *testing.T) {
+	hc := prepareHandlerContext(t)
+
+	bktName, objName := "bucket-1", "object-1"
+	createBucketAndObject(hc, bktName, objName)
+
+	for _, tc := range []struct {
+		name  string
+		body  *Tagging
+		error bool
+	}{
+		{
+			name: "Two tags with unique keys",
+			body: &Tagging{
+				TagSet: []Tag{
+					{
+						Key:   "key-1",
+						Value: "val-1",
+					},
+					{
+						Key:   "key-2",
+						Value: "val-2",
+					},
+				},
+			},
+			error: false,
+		},
+		{
+			name: "Two tags with the same keys",
+			body: &Tagging{
+				TagSet: []Tag{
+					{
+						Key:   "key-1",
+						Value: "val-1",
+					},
+					{
+						Key:   "key-1",
+						Value: "val-2",
+					},
+				},
+			},
+			error: true,
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			w, r := prepareTestRequest(hc, bktName, objName, tc.body)
+			hc.Handler().PutObjectTaggingHandler(w, r)
+			if tc.error {
+				assertS3Error(t, w, apiErrors.GetAPIError(apiErrors.ErrInvalidTagKeyUniqueness))
+				return
+			}
+			assertStatus(t, w, http.StatusOK)
+
+			tagging := getObjectTagging(t, hc, bktName, objName, emptyVersion)
+			require.Len(t, tagging.TagSet, 2)
+			require.Equal(t, "key-1", tagging.TagSet[0].Key)
+			require.Equal(t, "val-1", tagging.TagSet[0].Value)
+			require.Equal(t, "key-2", tagging.TagSet[1].Key)
+			require.Equal(t, "val-2", tagging.TagSet[1].Value)
+		})
+	}
+}