diff --git a/README.md b/README.md
index 70a2d86..ab158a4 100644
--- a/README.md
+++ b/README.md
@@ -26,6 +26,7 @@ if err != nil {
 
 * [x] GET /api/v1/accounts/:id
 * [x] GET /api/v1/accounts/verify_credentials
+* [ ] PATCH /api/v1/accounts/update_credentials
 * [x] GET /api/v1/accounts/:id/followers
 * [x] GET /api/v1/accounts/:id/following
 * [ ] GET /api/v1/accounts/:id/statuses
diff --git a/accounts.go b/accounts.go
index 3de8000..fa94a1f 100644
--- a/accounts.go
+++ b/accounts.go
@@ -46,6 +46,42 @@ func (c *Client) GetAccountCurrentUser() (*Account, error) {
 	return &account, nil
 }
 
+// Profile is a struct for updating profiles.
+type Profile struct {
+	// If it is nil it will not be updated.
+	// If it is empty, update it with empty.
+	DisplayName *string
+	Note        *string
+
+	// Set the base64 encoded character string of the image.
+	Avatar string
+	Header string
+}
+
+// AccountUpdate updates the information of the current user.
+func (c *Client) AccountUpdate(profile *Profile) (*Account, error) {
+	params := url.Values{}
+	if profile.DisplayName != nil {
+		params.Set("display_name", *profile.DisplayName)
+	}
+	if profile.Note != nil {
+		params.Set("note", *profile.Note)
+	}
+	if profile.Avatar != "" {
+		params.Set("avatar", profile.Avatar)
+	}
+	if profile.Header != "" {
+		params.Set("header", profile.Header)
+	}
+
+	var account Account
+	err := c.doAPI(http.MethodPatch, "/api/v1/accounts/update_credentials", params, &account)
+	if err != nil {
+		return nil, err
+	}
+	return &account, nil
+}
+
 // GetAccountFollowers return followers list.
 func (c *Client) GetAccountFollowers(id int64) ([]*Account, error) {
 	var accounts []*Account
diff --git a/accounts_test.go b/accounts_test.go
index 0dc8a82..e7bc167 100644
--- a/accounts_test.go
+++ b/accounts_test.go
@@ -7,6 +7,33 @@ import (
 	"testing"
 )
 
+func TestAccountUpdate(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprintln(w, `{"Username": "zzz"}`)
+		return
+	}))
+	defer ts.Close()
+
+	client := NewClient(&Config{
+		Server:       ts.URL,
+		ClientID:     "foo",
+		ClientSecret: "bar",
+		AccessToken:  "zoo",
+	})
+	a, err := client.AccountUpdate(&Profile{
+		DisplayName: String("display_name"),
+		Note:        String("note"),
+		Avatar:      "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAUoAAADrCAYAAAA...",
+		Header:      "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAUoAAADrCAYAAAA...",
+	})
+	if err != nil {
+		t.Fatalf("should not be fail: %v", err)
+	}
+	if a.Username != "zzz" {
+		t.Fatalf("want %q but %q", "zzz", a.Username)
+	}
+}
+
 func TestGetBlocks(t *testing.T) {
 	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		fmt.Fprintln(w, `[{"Username": "foo"}, {"Username": "bar"}]`)
diff --git a/helper.go b/helper.go
new file mode 100644
index 0000000..c9fefe9
--- /dev/null
+++ b/helper.go
@@ -0,0 +1,38 @@
+package mastodon
+
+import (
+	"encoding/base64"
+	"net/http"
+	"os"
+)
+
+// Base64EncodeFileName returns the base64 data URI format string of the file with the file name.
+func Base64EncodeFileName(filename string) (string, error) {
+	file, err := os.Open(filename)
+	if err != nil {
+		return "", err
+	}
+	defer file.Close()
+
+	return Base64Encode(file)
+}
+
+// Base64Encode returns the base64 data URI format string of the file.
+func Base64Encode(file *os.File) (string, error) {
+	fi, err := file.Stat()
+	if err != nil {
+		return "", err
+	}
+
+	d := make([]byte, fi.Size())
+	_, err = file.Read(d)
+	if err != nil {
+		return "", err
+	}
+
+	return "data:" + http.DetectContentType(d) +
+		";base64," + base64.StdEncoding.EncodeToString(d), nil
+}
+
+// String is a helper function to get the pointer value of a string.
+func String(v string) *string { return &v }
diff --git a/helper_test.go b/helper_test.go
new file mode 100644
index 0000000..a4a6429
--- /dev/null
+++ b/helper_test.go
@@ -0,0 +1,13 @@
+package mastodon
+
+import (
+	"testing"
+)
+
+func TestString(t *testing.T) {
+	s := "test"
+	sp := String(s)
+	if *sp != s {
+		t.Fatalf("want %q but %q", s, *sp)
+	}
+}
diff --git a/mastodon.go b/mastodon.go
index a8660ab..e3fbb88 100644
--- a/mastodon.go
+++ b/mastodon.go
@@ -36,6 +36,9 @@ func (c *Client) doAPI(method string, uri string, params url.Values, res interfa
 		return err
 	}
 	req.Header.Set("Authorization", "Bearer "+c.config.AccessToken)
+	if params != nil {
+		req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+	}
 	resp, err = c.Do(req)
 	if err != nil {
 		return err