The right-hander spent eight seasons with the Blue Jays before the club dealt him to the Chicago White Sox last July 27. The Sox sent him back to Toronto on Sunday and picked up pitching prospects Daniel Webb and Myles Jaye in return from the Jays.
Frasor made a combined 64 relief appearances for the Jays and White Sox last season, posting a record of 3-4 with a 3.60 earned run average. In his first stint with Toronto, he was 24-28 with 36 saves and a 3.69 ERA in 455 games.
The White Sox will pick up a pair of right-handed hurlers who have not pitched above Class-A ball.
Jaye, who turned 20 on December 28, made his pro debut in 2011 and was 3-3 with a 3.00 ERA at Bluefield of the Appalachian League. Webb, 22, spent most of 2011 with Single-A Lansing and was 4-5 with a 5.48 ERA.