Both were signed out of the Dominican Republic, and they are not related to each other or former Red Sox player Israel Alcantara -- an outfielder and first baseman in 2000 and '01 -- the Web site reported.
Raul Alcantara is considered one of the better pitchers available during the international signing period, which started Thursday. The roughly 6-foot-3 right-hander, who sports a mid- to high-80s fastball, is believed to have signed for about $500,000.
Mario Alcantara, also about 6-foot-3 and a righty, is said to sport a high-80s fastball and curveball and is believed to have signed for about $350,000.
Boston has also signed right-handed pitcher Chez Angeloni to a free-agent contract, according to The Baltimore Sun.
Angeloni, a recent graduate of Johns Hopkins University, was the Most Outstanding Player of the 2008 NCAA Division III College World Series.
Alden Gonzalez is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.