The team announced the signing Monday.
The 32-year old Sizemore was released by Philadelphia earlier this month.
Sizemore will report to the Rays' spring training complex in Port Charlotte, Fla., this week to start working out. No date has been set for when he will play in minor league games.
He has a .265 average with 144 homers and 491 RBIs during a 10-year big league career.