diff --git a/weed/s3api/s3api_object_handlers_postpolicy.go b/weed/s3api/s3api_object_handlers_postpolicy.go
index 8ebcc71097..78fdedd8d0 100644
--- a/weed/s3api/s3api_object_handlers_postpolicy.go
+++ b/weed/s3api/s3api_object_handlers_postpolicy.go
@@ -88,6 +88,9 @@ func (s3a *S3ApiServer) PostPolicyBucketHandler(w http.ResponseWriter, r *http.R
 	}
 	if identity != nil {
 		r = r.WithContext(recordIdentityInContext(r, identity))
+		if identity.Account != nil {
+			r.Header.Set(s3_constants.AmzAccountId, identity.Account.Id)
+		}
 	}
 
 	policyBytes, err := base64.StdEncoding.DecodeString(formValues.Get("Policy"))
@@ -156,12 +159,19 @@ func (s3a *S3ApiServer) PostPolicyBucketHandler(w http.ResponseWriter, r *http.R
 	versioningState, err := s3a.getVersioningState(bucket)
 	if err != nil {
 		if errors.Is(err, filer_pb.ErrNotFound) {
-			s3err.WriteErrorResponse(w, r, s3err.ErrNoSuchBucket)
+			// Auto-create bucket if it doesn't exist (requires Admin permission)
+			if !s3a.handleAutoCreateBucket(w, r, bucket, "PostPolicyBucketHandler") {
+				return
+			}
+			// Re-fetch versioning state to handle race conditions where
+			// another process might have created the bucket with versioning enabled.
+			versioningState, err = s3a.getVersioningState(bucket)
+		}
+		if err != nil {
+			glog.Errorf("PostPolicyBucketHandler: versioning state for bucket %s: %v", bucket, err)
+			s3err.WriteErrorResponse(w, r, s3err.ErrInternalError)
 			return
 		}
-		glog.Errorf("PostPolicyBucketHandler: versioning state for bucket %s: %v", bucket, err)
-		s3err.WriteErrorResponse(w, r, s3err.ErrInternalError)
-		return
 	}
 	objectLockEnabled, err := s3a.isObjectLockEnabled(bucket)
 	if err != nil && !errors.Is(err, filer_pb.ErrNotFound) {
diff --git a/weed/s3api/s3api_object_handlers_postpolicy_authz_test.go b/weed/s3api/s3api_object_handlers_postpolicy_authz_test.go
index a0e0f7e4ce..c341979181 100644
--- a/weed/s3api/s3api_object_handlers_postpolicy_authz_test.go
+++ b/weed/s3api/s3api_object_handlers_postpolicy_authz_test.go
@@ -14,6 +14,7 @@ import (
 	"time"
 
 	"github.com/gorilla/mux"
+	"github.com/seaweedfs/seaweedfs/weed/pb/filer_pb"
 	"github.com/seaweedfs/seaweedfs/weed/pb/iam_pb"
 	"github.com/seaweedfs/seaweedfs/weed/s3api/s3_constants"
 	"github.com/seaweedfs/seaweedfs/weed/s3api/s3err"
@@ -37,6 +38,9 @@ const (
 	postPolicySecretKey = "secret-key-for-policy-only"
 	postReadAccessKey   = "AKIAPOLICYREAD0000"
 	postReadSecretKey   = "secret-key-for-policy-read"
+
+	postAdminAccessKey = "AKIAADMINTEST000"
+	postAdminSecretKey = "secret-key-for-admin-tests"
 )
 
 // newPostAuthzServer builds an S3ApiServer whose non-admin "tester" identity
@@ -394,3 +398,100 @@ func TestPostPolicyAttachedPolicyDeny(t *testing.T) {
 		"POST from a read-only identity must stay AccessDenied, body: %s", rec.Body.String())
 	assert.Contains(t, rec.Body.String(), "AccessDenied")
 }
+
+// newPostAutoCreateServer builds an S3ApiServer on the fake filer with
+// auto-create enabled, an "admin" identity allowed to create buckets, and the
+// non-admin "tester" writer.
+func newPostAutoCreateServer(t *testing.T, filer *ambiguousPutFiler) *S3ApiServer {
+	t.Helper()
+
+	iam := &IdentityAccessManagement{
+		hashes:       make(map[string]*sync.Pool),
+		hashCounters: make(map[string]*int32),
+	}
+	err := iam.loadS3ApiConfiguration(&iam_pb.S3ApiConfiguration{
+		Identities: []*iam_pb.Identity{{
+			Name:        "admin",
+			Account:     &iam_pb.Account{Id: "000000000000", DisplayName: "admin"},
+			Credentials: []*iam_pb.Credential{{AccessKey: postAdminAccessKey, SecretKey: postAdminSecretKey}},
+			Actions:     []string{"Admin"},
+		}, {
+			Name:        "tester",
+			Account:     &iam_pb.Account{Id: "000000000000", DisplayName: "tester"},
+			Credentials: []*iam_pb.Credential{{AccessKey: postAuthzAccessKey, SecretKey: postAuthzSecretKey}},
+			Actions:     []string{"Read:" + postAuthzBucket, "Write:" + postAuthzBucket, "List:" + postAuthzBucket},
+		}},
+	})
+	require.NoError(t, err)
+
+	s3a := newFailoverTestServer(t, startFakeFiler(t, filer))
+	s3a.iam = iam
+	s3a.option.BucketsPath = "/buckets"
+	s3a.option.AutoCreateBucket = true
+	s3a.bucketConfigCache = NewBucketConfigCache(time.Minute)
+	return s3a
+}
+
+// A signed POST Object upload to a bucket that does not exist must lazy-create
+// it the way PutObject does: an admin signer is allowed to create the bucket
+// and the upload proceeds against it, landing the object entry and its chunk
+// instead of answering NoSuchBucket.
+func TestPostPolicyBucketHandlerAutoCreatesMissingBucket(t *testing.T) {
+	volume := startFakeVolumeServer(t)
+	filer := &ambiguousPutFiler{
+		volume:  volume,
+		entries: map[string]*filer_pb.Entry{},
+		apply:   true,
+	}
+	s3a := newPostAutoCreateServer(t, filer)
+
+	rec := httptest.NewRecorder()
+	s3a.PostPolicyBucketHandler(rec, newSignedPostRequestFor(t, "uploads/pic.png",
+		postAdminAccessKey, postAdminSecretKey, map[string]string{"success_action_status": "201"}))
+
+	assert.Equal(t, http.StatusCreated, rec.Code,
+		"POST to a missing bucket must complete the upload after creating it, body: %s", rec.Body.String())
+	assert.Contains(t, rec.Body.String(), "<Key>uploads/pic.png</Key>")
+
+	filer.mu.Lock()
+	defer filer.mu.Unlock()
+	bucketEntry := filer.entries["/buckets/"+postAuthzBucket]
+	require.NotNil(t, bucketEntry, "POST to a missing bucket must create it like PUT")
+	assert.True(t, bucketEntry.IsDirectory)
+	assert.Equal(t, []byte("admin"), bucketEntry.Extended[s3_constants.AmzIdentityId])
+	assert.Equal(t, []byte("000000000000"), bucketEntry.Extended[s3_constants.ExtAmzOwnerKey])
+	objectEntry := filer.entries["/buckets/"+postAuthzBucket+"/uploads/pic.png"]
+	require.NotNil(t, objectEntry, "the upload must land its object entry on the new bucket")
+	assert.NotEmpty(t, objectEntry.Chunks)
+
+	volume.mu.Lock()
+	defer volume.mu.Unlock()
+	var stored []byte
+	for _, data := range volume.stored {
+		stored = append(stored, data...)
+	}
+	assert.Contains(t, string(stored), "payload", "the file body must reach the assigned volume")
+}
+
+// A non-admin signer keeps the PUT semantics: the upload itself is authorized
+// but the lazy create is refused, surfacing AccessDenied rather than creating
+// the bucket or answering NoSuchBucket.
+func TestPostPolicyBucketHandlerAutoCreateDeniedForNonAdmin(t *testing.T) {
+	volume := startFakeVolumeServer(t)
+	filer := &ambiguousPutFiler{
+		volume:  volume,
+		entries: map[string]*filer_pb.Entry{},
+		apply:   true,
+	}
+	s3a := newPostAutoCreateServer(t, filer)
+
+	rec := httptest.NewRecorder()
+	s3a.PostPolicyBucketHandler(rec, newSignedPostRequestFor(t, "uploads/pic.png", postAuthzAccessKey, postAuthzSecretKey, nil))
+
+	assert.Equal(t, http.StatusForbidden, rec.Code, "body: %s", rec.Body.String())
+	assert.Contains(t, rec.Body.String(), "AccessDenied")
+
+	filer.mu.Lock()
+	defer filer.mu.Unlock()
+	assert.Empty(t, filer.entries, "a non-admin POST must not create the bucket")
+}