- Name: Sato Masaki (佐藤優樹)
- Nicknames: Masaki (まさき), Maachan (まーちゃん), Masa (まさ), Masaking (まさキング)
- Birthday: May 7, 1999
- Birthplace: Hokkaido, Japan
- Blood type: A
- Hobbies: Playing drums, riding horses
- Specialties: Piano, ballet
- Favorite Food: Soba, udon, plum sheets
- Favorite Color: Yellow, green
- Looks Up To: Niigaki Risa, Takahashi Ai
- Hello! Project groups:
The tenth generation made their official presentation on the same day they were announced as new members in the "Morning Musume Concert Tour Fall 2011 Ai Believe ~Takahashi Ai Graduation Memory Special~" concert, and they participated in a performance of the song "Tomo".
- [2012.07.11] Greeting ~Sato Masaki~ (Greeting ～佐藤優樹～)
- [2013.01.16] Alo Hello! Morning Musume 9 10ki DVD (Fukumura Mizuki, Ikuta Erina, Sayashi Riho, Suzuki Kanon, Iikubo Haruna, Ishida Ayumi, Sato Masaki, Kudo Haruka)
- [2012.09.10] Morning Musume｡ 9・10ki 1st official Photo Book (モーニング娘。9・10期 1st official Photo Book) (Fukumura Mizuki, Ikuta Erina, Sayashi Riho, Suzuki Kanon, Iikubo Haruna, Ishida Ayumi, Sato Masaki, Kudo Haruka)
- [2013.01.16] Alo Hello! Morning Musume 10ki Photobook (アロハロ！モーニング娘。10期メンバー写真集) (Iikubo Haruna, Ishida Ayumi, Sato Masaki, Kudo Haruka)
- [2013.09.30] Morning Musume 15th Anniversary Photobook ZERO (モーニング娘。 15th Anniversary Photobook ZERO) (Michishige Sayumi, Fukumura Mizuki, Ikuta Erina, Sayashi Riho, Suzuki Kanon, Iikubo Haruna, Ishida Ayumi, Sato Masaki, Kudo Haruka, Oda Sakura)
- [2014.05.30] Michishige Camera '13-'14 (ミチシゲカメラ'13-'14) (Michishige Sayumi, Fukumura Mizuki, Ikuta Erina, Sayashi Riho, Suzuki Kanon, Iikubo Haruna, Ishida Ayumi, Sato Masaki, Kudo Haruka, Oda Sakura)
- TV Programs
- [2011–2012] HELLOPRO! TIME (ハロプロ！ＴＩＭＥ)
- [2012–2013] Hello! SATOYAMA Life (ハロー！ＳＡＴＯＹＡＭＡライフ)
- [2014–] The Girls Live
- TV Dramas
-  Suugaku♥Joushi Gakuen (数学♥女子学園)
-  Michishige Sayumi no "Mobekimasutte Nani??" (道重さゆみの『モベキマスってなに？？』)
-  Guest, Maachan (ゲスト、まぁちゃん。)
-  Stacy's Shoujo Saisatsu Kageki (ステーシーズ 少女再殺歌劇)
-  Idol Nihonryuu ~Onna Nichibu~ (アイドル日本流～おんな日舞～)
-  LILIUM -Lilium Shoujo Junketsu Kageki- (LILIUM －リリウム 少女純潔歌劇－)
- [2012–] Morning Musume no Morning Jogakuin ~Houkago Meeting~ (モーニング娘。のモーニング女学院～放課後ミーティング～)
- Her official Morning Musume image color is emerald green.
- She is the sixth Morning Musume member to come from Hokkaido, after Ishiguro Aya, Iida Kaori, Abe Natsumi, Konno Asami, and Fujimoto Miki.
- Her favorite word is "deshou" (でしょう; "right?").
- Her motto is "Don't be noisy".
- Her philosophy is "being smiley".
- She believes she can't lose at having perfect pitch.
- She is left-handed.
- Has played the piano since she was 2 years old.
- Played the drums starting in her third year of elementary school, but stopped two years ago as of 2012.
- Is practiced to competition level obstacle jumping in horse back riding.
- Considers her charm point to be her eyelashes.
- Noted her favorite Morning Musume song to be "Maji Desu ka Ska!" in 2011, and "Fantasy ga Hajimaru" in 2012.
- Calls her father "Chichi" (父父) instead of "Papa" or "Otousan" (お父さん).
- Has two younger sisters.
- Has said that if she were not a member of Morning Musume, she would want to be a piano teacher.
- Spoke English until she was 5 years old, when she began kindergarten and had to start speaking Japanese. She grew up watching Disney Channel shows in English, and still does, despite no longer understanding the language.
- Notably called Tanaka Reina "Tanasatan" (たなさたん).