The unsteady cavitation such as rotating cavitation and cavitation surge often occur in the turbopump inducers for rocket engine. In the present study, a method for suppressing the unsteady cavitation in an inducer by jet injection is proposed. Through eight nozzles placed at the upstream of the inducer, jet was injected in circumferential direction. The axial position of nozzles, speed of jet flow and direction of jet injection were changed. Through the experiments with jet injection for various conditions, it was found that the occurrence regions of unsteady cavitation are decreased significantly by jet injection in the same direction as shaft rotation with the jet flow rate about 10% of total flow. The flow field was also examined to clarify the mechanism for suppressing the unsteady cavitation by jet injection. It was found that the incidence angle and cavity length was reduced by jet injection which decreases occurrence regions of unsteady cavitation.