KMRJ was launched in July 1998 as "M99.5" under an alternative rock format. It switched to a classic rock format as "The Heat" in July 2008. In October 2009, ownership changed from Mitchell Media to RM Broadcasting, owners of KPLM, KJJZ (now KRHQ) and KAJR (now KJJZ). Studios were relocated as well.
On August 31, 2012, after playing Wild Cherry's "Play That Funky Music" over and over for several hours, KMRJ flipped formats to Rhythmic oldies as "Jammin' 99.5," with an emphasis on Rhythmic hits and Old School classics.