A roster spot opened when Red Sox left fielder Jason Bay filed for free agency.
Hermida, 25, the 11th overall pick in the 2002 Player Draft by the Marlins, is a .265 career hitter with 57 homers and 210 RBI. Last season, he hit .259 with 13 homers and 47 RBI, but struck out 101 times in 429 at-bats.
"Hermida is a player who hasn't fulfilled his potential yet," General Manager Theo Epstein said on Boston's Web site. "His minor league track record, his age, draft pedigree, our scouting reports over the years, indicate that there's a chance he can turn into the player that he was once thought to be."
Copyright 2009 by United Press International.