The injection and relaxation of electron spins in In0.1Ga0.9N film were studied by femtosecond time-resolved circularly polarized pump-probe spectroscopy. An initial degree of spin polarization of 02 was obtained, which agrees with 3∶1 ratio of heavy- to light-hole valence bands in transition strength, but not with the 1∶1 or 1∶0.94 ratios. A spin relaxation lifetime of 490±70ps was obtained at room temperature. The spin relaxation mechanism is discussed qualitatively, and is thought to be dominated by BAP mechanism here.