Kao refused to sign a long-term contract with Uni-President Lions in 2012, having the confidence that he would perform better the next season.[2] Before 2013 season, he claimed that he did not regret about not signing a long-term with Uni-President Lions the previous year.[3]
Kao did not play for the Lions in 2023, and was non–tendered by the team on November 30, 2023.[4]
On May 27, 2024, Kao announced his retirement from professional baseball, and ended his career by playing in one final game for Lions, in which he went 0–for–4 with one RBI and three strikeouts.[5]