Uehara, who helped the Texas Rangers reach the 2011 World Series, missed over a month of last season with a right lat strain but still posted a stingy 1.75 earned-run average while striking out 43 batters in 36 innings.
"First, I am really grateful for the Boston Red Sox expressing the strong desire to acquire me and giving this new opportunity," Uehara, who signed a one-year contract with Boston worth a reported $4.25 million, said on the Red Sox website.
"Now it's my responsibility to meet their expectation and to give my best performance without getting injured."
Twice a winner of the Sawamura Award as the best starting pitcher in Japan with the Yomiuri Giants, Uehara has spent most of his MLB coming out of the bullpen as a closer and reliever.
The 37-year-old pitcher broke into the majors with the Baltimore Orioles in 2009 and was traded to the Rangers midway through the 2011 season. (Reporting by Steve Keating in Toronto; Editing by Frank Pingue)
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