An exemplary heat sink mounting frame is for mounting a heat sink onto a circuit board. The heat sink mounting frame includes a circular guide rail, and mounting arms movably connected with and extending radially and outwardly from the guide rail. Each mounting arm includes a fixing bracket connected to the guide rail and a sliding bar slidably connected with the fixing bracket. An engaging post is formed on the sliding bar. The sliding bar is slidable along the fixing bracket, such that a total length of each of the mounting arms is variable to adjust the locations of the engaging posts of the mounting arms.