Cut last month by the Los Angeles Dodgers, the 36-year-old righty signed a one-year deal with the AL Central leaders to be a long reliever and spot starter.
"Coming back I really feel great and the White Sox again gave me a great opportunity to bounce back for the past two years after what I've been through and I just want to give it my best," Loaiza said.
Loaiza made 55 starts for the White Sox from 2003-04. He was the AL's starting pitcher in the 2003 All-Star Game at U.S Cellular Field, and went 21-9 with a 2.90 ERA while leading the league in strikeouts.
Loaiza was traded to the New York Yankees on July 31, 2004, for Jose Contreras. Since the deal, Loaiza has struggled with problems in both shoulders, resulting in four separate stints on the disabled list.
This year, Loaiza made seven appearances, including three starts, and was 1-2 with a 5.63 ERA for the Dodgers. He was designated for assignment after being activated from the disabled list, having been sidelined because of tightness in his shoulder blade.
Loaiza is 126-114 over his 13 major league seasons and has a career ERA of 4.65. He has also pitched for the Pirates, Rangers, Blue Jays, Yankees, Nationals and A's.
"I'm just ready to do the best possible in the bullpen or as a starter," Loaiza said. "Right now, I think I'm in long relief."
Loaiza will allow the White Sox to move Nick Masset into a more of a setup role and provide depth for Octavio Dotel and Scott Linebrink.
"It's just a desire to push him back a little bit but also cover our rotation with another long guy in the bullpen," White Sox general manager Kenny Williams said.
To make room for Loaiza, the White Sox optioned reliever Ehren Wasserman to Triple-A Charlotte. He was 0-1 with a 14.85 ERA in 11 relief appearances with the White Sox after being recalled from Charlotte on April 27.
The White Sox also announced that outfielder DeWayne Wise had accepted an outright assignment to Charlotte. He was designated for assignment on May 31 after appearing in six games with the White Sox.