We report on an ultralow-threshold Raman laser based on a CaF 2 whispering-gallery-mode resonator. The laser is demonstrated to have a conversion efficiency above 60%. The observed low lasing threshold is made possible by the ultrahigh optical quality factor of the cavity, which is on the order of Q =10 10 . The laser is fibercompatible and is fabricated with a very simple technique. We also demonstrate a single-mode operation of the laser in a multimode cavity as well as a multimode operation of the laser in a single-mode cavity.