A study of the polymerization of some vinyl monomers by the system of N-bromosuccinimide (NBS) and reduced nickel was made at 60°C. It was found that this system shows excellent activity for methyl methacrylate, weak activity for styrene, and no effect for vinyl acetate polymerizations. From the results of the polymerization kinetics, the copolymerization experiment, and the effect of radical inhibitors, it was proved that polymerization by this initiator system proceeds via a radical intermediate. The initiation is considered to be induced by a succinimide radical that is produced. The mechanism for initiation is presented and discussed.