Mn/Sb multilayer films were grown on (100) GaAs substrate by an ultrahigh vacuum evaporation system and were annealed for a short time. The magnetic and magneto-optical properties were investigated for the samples unannealed and annealed, respectively. All unannealed Mn/Sb multilayer f ilms exhibit strong ferromagnetic properties and the easy magnetization axes are in-plane. The surface of the samples consists of dense islands. The longitudin al (H∥ plane) Kerr effect was not observed for the unannealed samples. All samples annealed at 350℃ for 20min were found to be single phase with nickel ar senide (NiAs) crystal structure and have the largest saturation magnetization Ms and the lowest coercive force Hc. The magnetic force microscope ima ge shows uniform ferromagnetic properties of the film. The longitudinal magneto -optical Kerr effect was observed. The observable Kerr effect hysteresis loop c an be obtained for the annealed Mn/Sb multilayer films on GaAs.