The 35-year-old Treanor was a fourth-round selection by the Royals in the 1994 draft and traded to Florida in 1997 for right-hander Matt Whisenant. He appeared in 82 games last year for the Rangers and hit a home run off the New York Yankees in the ALCS.
He's a seven-year major league veteran with a career average of .227 in 360 games for the Marlins, Tigers and Rangers. He was 6 for 22 with one home run and four RBIs in 11 games for the Rangers this spring.
The Royals are unsettled at catcher while they wait for the return from surgery of Jason Kendall, who could be back by late April.