Neither benzyl chloride nor N，N-dimethylaniline is an initmtor for vinyl polymeriza-tion．When these compounds are used together，they will act as an'effective initiator．For studying the effects of the concentration of the initiator，temperature and the solvents the polymerization rates of methyl methacrylate have been determined．In the initiation systems CHa-xClx+ N CH3 CH3 x=1，2，3，the larger is the x，the greater is the initiation rate．The initiation rates of the binary mixture and the quaternary ammonium salt prepared from this binary sys-tom were compared．Thus a mechanism for vinyl polymerization initiated by this system is proposed and the rate equation derived as—d[m]-dt=Kp(ki-kt)1-2[DMA]1-2[BzCl]1-2[M]．The activation energy of initiation is calculated to be 13．2 kcal／mole in the temperature range from 50 to 70℃．