Sizemore, who served as a graduate assistant coach for the Cougars in 2012, will replace Brent Walsh who was with College of Charleston for the past four seasons.
"I am extremely excited about hiring Brandon Sizemore as an assistant coach," Lee said. "Brandon is one of the best players to ever play here and will be a great asset to our program as a former Cougar. He will be assisting with the hitters and work with infielders as well as running camps."
Sizemore played for the Cougars in 2008 and 2009 where he was a NCBWA First Team All-American, All-Southern Conference selection, and Second Team ACBA All-Region honoree. In 2009, Sizemore led the team with 74 RBI, while his 82 RBI in 2008 ranked seventh nationally.
He finished with a .321 batting average for his career, to go with 37 home runs and 156 RBI.
A native of Jacksonville, Fla., Sizemore was selected by the Milwaukee Brewers in the 30th round of the 2009 MLB Entry Draft. He played for two years with the Arizona Brewers, Wisconsin Timber Rattlers and the Helena Brewers.