Since he joined Boston from Minnesota in 2003, Ortiz, 30, has become one of the most productive players in the Major League Baseball.
The designated hitter has 119 home runs and 388 RBI in three seasons with the Red Sox.
Last season he was second to Alex Rodriguez, of the New York Yankees, in the American League MVP race, batting .300 with 47 home runs and 148 RBI.
Ortiz was voted MVP of the AL Championship Series in 2004, when Boston came back from an 0-3 deficit to defeat the Yankees in seven games and advance to the World Series. The Red Sox then swept the St. Louis Cardinals for their first title since 1918.
Ortiz will earn $6.5 million in 2006, the second year of a two-year, $12.5 million contract signed in May 2004. The team has a $7.7 million option on him for 2007.