- Name: Sato Masaki (佐藤優樹)
- Nicknames: Masaki (まさき), Maachan (まーちゃん)
- 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)
- TV Programs
- [2011–2012] HELLOPRO! TIME (ハロプロ！ＴＩＭＥ)
- 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～)
- [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 philosphy is "being smiley".
- She believes she can't lose at having perfect pitch.
- She is left handed.
- Has practiced playing the piano since she was 2 years old.
- Practiced 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 using Japanese.
- She grew up watching Disney Channel shows in English, and still does (despite no longer understanding the language).
- Hello! Project Profile
- Morning Musume 10th Generation Official Blog
- Wikipedia Profiles: Japanese: 佐藤優樹 | English: Masaki Sato