There are 10 Japanese MLB players played for the Boston Red Sox
Naoyuki
Uwasawa
RHP 
Boston Red Sox
(Hokkaido Nippon Ham Fighters, Tampa Bay Rays, Boston Red Sox )
上沢直之 (うわさわ・なおゆき)
Bats: R Throws: R
Current Age 30
(187cm, 88kg)
MLB Debut: Not Yet
Masataka
Yoshida
(ORIX Buffaloes, Boston Red Sox )
吉田正尚 (よしだ・まさたか)
Bats: L Throws: R
Current Age 30
5-8, 192lb (173cm, 87kg)
MLB Debut:
2023-03-30 (29)
Hirokazu
Sawamura
(Yomiuri Giants, Chiba Lotte Marines, Boston Red Sox )
澤村拓一 (さわむら・ひろかず)
Bats: R Throws: R
Current Age 36
6-0, 212lb (183cm, 96kg)
MLB Debut:
2021-04-02 (32)
Junichi
Tazawa
RHP Boston Red Sox
(Boston Red Sox , Miami Marlins, Los Angeles Angels)
田沢純一 (たざわ・じゅんいち)
Bats: R Throws: R
Current Age 37
5-11, 200lb (180cm, 90kg)
MLB Debut:
2009-08-07 (23)
Koji
Uehara
RHP Boston Red Sox
(Baltimore Orioles, Texas Rangers, Boston Red Sox , Chicago Cubs, Yomiuri Giants)
上原浩治 (うえはら・こうじ)
Bats: R Throws: R
Current Age 49
6-2, 195lb (188cm, 88kg)
MLB Debut:
2009-04-08 (34)
Daisuke
Matsuzaka
RHP Boston Red Sox
(Saitama Seibu Lions, Boston Red Sox , New York Mets, Fukuoka SoftBank Hawks, Chunichi Dragons)
松坂大輔 (まつざか・だいすけ)
Bats: R Throws: R
Current Age 43
6-0, 205lb (183cm, 92kg)
MLB Debut:
2007-04-05 (26)
Hideki
Okajima
LHP Boston Red Sox
(Boston Red Sox , Oakland Athletics, Yomiuri Giants, Hokkaido Nippon Ham Fighters, Fukuoka SoftBank Hawks, Yokohama DeNA BayStars)
岡島秀樹 (おかじま・ひでき)
Bats: L Throws: L
Current Age 48
6-1, 195lb (185cm, 88kg)
MLB Debut:
2007-04-02 (31)
Takashi
Saito
(Los Angeles Dodgers, Boston Red Sox , Atlanta Braves, Milwaukee Brewers, Arizona Diamondbacks, Yokohama DeNA BayStars, Tohoku Rakuten Golden Eagles)
斎藤隆 (さいとう・たかし)
Bats: L Throws: R
Current Age 54
6-2, 200lb (188cm, 90kg)
MLB Debut:
2006-04-09 (36)
Tomokazu
Ohka
RHP Boston Red Sox
(Boston Red Sox , Montreal Expos, Washington Nationals, Milwaukee Brewers, Toronto Blue Jays, Cleveland Indians, Yokohama DeNA BayStars)
大家友和 (おおか・ともかず)
Bats: S Throws: R
Current Age 48
6-1, 205lb (185cm, 92kg)
MLB Debut:
1999-07-19 (23)
Hideo
Nomo
(Los Angeles Dodgers, New York Mets, Osaka Kintetsu Buffaloes, Milwaukee Brewers, Detroit Tigers, Boston Red Sox , Tampa Bay Rays, Kansas City Royals)
野茂英雄 (のも・ひでお)
Bats: R Throws: R
Current Age 55
6-2, 210lb (188cm, 95kg)
MLB Debut:
1995-05-02 (26)