diff --git a/weed/s3api/filer_multipart.go b/weed/s3api/filer_multipart.go
index 1514e2aa8..5a039382b 100644
--- a/weed/s3api/filer_multipart.go
+++ b/weed/s3api/filer_multipart.go
@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"github.com/chrislusf/seaweedfs/weed/s3api/s3err"
 	"path/filepath"
+	"sort"
 	"strconv"
 	"strings"
 	"time"
@@ -62,10 +63,15 @@ type CompleteMultipartUploadResult struct {
 	s3.CompleteMultipartUploadOutput
 }
 
-func (s3a *S3ApiServer) completeMultipartUpload(input *s3.CompleteMultipartUploadInput) (output *CompleteMultipartUploadResult, code s3err.ErrorCode) {
+func (s3a *S3ApiServer) completeMultipartUpload(input *s3.CompleteMultipartUploadInput, parts *CompleteMultipartUpload) (output *CompleteMultipartUploadResult, code s3err.ErrorCode) {
 
 	glog.V(2).Infof("completeMultipartUpload input %v", input)
 
+	completedParts := parts.Parts
+	sort.Slice(completedParts, func(i, j int) bool {
+		return completedParts[i].PartNumber < completedParts[j].PartNumber
+	})
+
 	uploadDirectory := s3a.genUploadsFolder(*input.Bucket) + "/" + *input.UploadId
 
 	entries, _, err := s3a.list(uploadDirectory, "", "", false, maxPartsList)
@@ -80,14 +86,16 @@ func (s3a *S3ApiServer) completeMultipartUpload(input *s3.CompleteMultipartUploa
 		return nil, s3err.ErrNoSuchUpload
 	}
 
+	mime := pentry.Attributes.Mime
+
 	var finalParts []*filer_pb.FileChunk
 	var offset int64
-	var mime string
 
 	for _, entry := range entries {
 		if strings.HasSuffix(entry.Name, ".part") && !entry.IsDirectory {
-			if entry.Name == "0001.part" && entry.Attributes.Mime != "" {
-				mime = entry.Attributes.Mime
+			_, found := findByPartNumber(entry.Name, completedParts)
+			if !found {
+				continue
 			}
 			for _, chunk := range entry.Chunks {
 				p := &filer_pb.FileChunk{
@@ -156,6 +164,20 @@ func (s3a *S3ApiServer) completeMultipartUpload(input *s3.CompleteMultipartUploa
 	return
 }
 
+func findByPartNumber(fileName string, parts []CompletedPart) (etag string, found bool) {
+	partNumber, formatErr := strconv.Atoi(fileName[:4])
+	if formatErr != nil {
+		return
+	}
+	x := sort.Search(len(parts), func(i int) bool {
+		return parts[i].PartNumber >= partNumber
+	})
+	if parts[x].PartNumber != partNumber {
+		return
+	}
+	return parts[x].ETag, true
+}
+
 func (s3a *S3ApiServer) abortMultipartUpload(input *s3.AbortMultipartUploadInput) (output *s3.AbortMultipartUploadOutput, code s3err.ErrorCode) {
 
 	glog.V(2).Infof("abortMultipartUpload input %v", input)
diff --git a/weed/s3api/filer_multipart_test.go b/weed/s3api/filer_multipart_test.go
index 9e1d2307b..52425b5b2 100644
--- a/weed/s3api/filer_multipart_test.go
+++ b/weed/s3api/filer_multipart_test.go
@@ -4,6 +4,7 @@ import (
 	"github.com/aws/aws-sdk-go/aws"
 	"github.com/aws/aws-sdk-go/service/s3"
 	"github.com/chrislusf/seaweedfs/weed/s3api/s3err"
+	"github.com/stretchr/testify/assert"
 	"testing"
 	"time"
 )
@@ -48,3 +49,85 @@ func TestListPartsResult(t *testing.T) {
 	}
 
 }
+
+func Test_findByPartNumber(t *testing.T) {
+	type args struct {
+		fileName string
+		parts    []CompletedPart
+	}
+
+	parts := []CompletedPart{
+		CompletedPart{
+			ETag:       "xxx",
+			PartNumber: 1,
+		},
+		CompletedPart{
+			ETag:       "yyy",
+			PartNumber: 3,
+		},
+		CompletedPart{
+			ETag:       "zzz",
+			PartNumber: 5,
+		},
+	}
+
+	tests := []struct {
+		name      string
+		args      args
+		wantEtag  string
+		wantFound bool
+	}{
+		{
+			"first",
+			args{
+				"0001.part",
+				parts,
+			},
+			"xxx",
+			true,
+		},
+		{
+			"second",
+			args{
+				"0002.part",
+				parts,
+			},
+			"",
+			false,
+		},
+		{
+			"third",
+			args{
+				"0003.part",
+				parts,
+			},
+			"yyy",
+			true,
+		},
+		{
+			"fourth",
+			args{
+				"0004.part",
+				parts,
+			},
+			"",
+			false,
+		},
+		{
+			"fifth",
+			args{
+				"0005.part",
+				parts,
+			},
+			"zzz",
+			true,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			gotEtag, gotFound := findByPartNumber(tt.args.fileName, tt.args.parts)
+			assert.Equalf(t, tt.wantEtag, gotEtag, "findByPartNumber(%v, %v)", tt.args.fileName, tt.args.parts)
+			assert.Equalf(t, tt.wantFound, gotFound, "findByPartNumber(%v, %v)", tt.args.fileName, tt.args.parts)
+		})
+	}
+}
diff --git a/weed/s3api/s3api_object_multipart_handlers.go b/weed/s3api/s3api_object_multipart_handlers.go
index 99c280e13..35bc174c8 100644
--- a/weed/s3api/s3api_object_multipart_handlers.go
+++ b/weed/s3api/s3api_object_multipart_handlers.go
@@ -1,11 +1,13 @@
 package s3api
 
 import (
+	"encoding/xml"
 	"fmt"
 	"github.com/chrislusf/seaweedfs/weed/glog"
 	xhttp "github.com/chrislusf/seaweedfs/weed/s3api/http"
 	"github.com/chrislusf/seaweedfs/weed/s3api/s3err"
 	weed_server "github.com/chrislusf/seaweedfs/weed/server"
+	"io"
 	"net/http"
 	"net/url"
 	"strconv"
@@ -56,8 +58,16 @@ func (s3a *S3ApiServer) NewMultipartUploadHandler(w http.ResponseWriter, r *http
 
 // CompleteMultipartUploadHandler - Completes multipart upload.
 func (s3a *S3ApiServer) CompleteMultipartUploadHandler(w http.ResponseWriter, r *http.Request) {
+	// https://docs.aws.amazon.com/AmazonS3/latest/API/API_CompleteMultipartUpload.html
+
 	bucket, object := xhttp.GetBucketAndObject(r)
 
+	parts := &CompleteMultipartUpload{}
+	if err := xmlDecoder(r.Body, parts, r.ContentLength); err != nil {
+		s3err.WriteErrorResponse(w, r, s3err.ErrMalformedXML)
+		return
+	}
+
 	// Get upload id.
 	uploadID, _, _, _ := getObjectResources(r.URL.Query())
 
@@ -65,7 +75,7 @@ func (s3a *S3ApiServer) CompleteMultipartUploadHandler(w http.ResponseWriter, r
 		Bucket:   aws.String(bucket),
 		Key:      objectKey(aws.String(object)),
 		UploadId: aws.String(uploadID),
-	})
+	}, parts)
 
 	glog.V(2).Info("CompleteMultipartUploadHandler", string(s3err.EncodeXMLResponse(response)), errCode)
 
@@ -268,8 +278,24 @@ func getObjectResources(values url.Values) (uploadID string, partNumberMarker, m
 	return
 }
 
-type byCompletedPartNumber []*s3.CompletedPart
+func xmlDecoder(body io.Reader, v interface{}, size int64) error {
+	var lbody io.Reader
+	if size > 0 {
+		lbody = io.LimitReader(body, size)
+	} else {
+		lbody = body
+	}
+	d := xml.NewDecoder(lbody)
+	d.CharsetReader = func(label string, input io.Reader) (io.Reader, error) {
+		return input, nil
+	}
+	return d.Decode(v)
+}
 
-func (a byCompletedPartNumber) Len() int           { return len(a) }
-func (a byCompletedPartNumber) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
-func (a byCompletedPartNumber) Less(i, j int) bool { return *a[i].PartNumber < *a[j].PartNumber }
+type CompleteMultipartUpload struct {
+	Parts []CompletedPart `xml:"Part"`
+}
+type CompletedPart struct {
+	ETag       string
+	PartNumber int
+}