The binary systems of N-acyloxyimides with p-toluenesulfonic acid (PTS) were found to serve as effective initiators for the radical polymerization of such vinyl monomers as methyl methacrylate (MMA), methyl acrylate, and acrylonitrile. N-Benzoyloxysuccinimide (NBS), N-acetoxysuccinimide, and N-benzoyloxyphthalimide were used as the N-acyloxyimides. The polymerization of MMA with the NBS/PTS system depended upon the solvents used. The results of copolymerization of MMA with styrene initiated by this system and of the application of the spin trapping technique indicated that polymerization proceeded through a radical mechanism. A kinetic study on the polymerization of MMA with this system in ethanol was also investigated. The observed overall activation energy was 18.2 kcal/mole. The rate of polymerization (Rp) was expressed as Rp= k[NBS]0.2[PTS]0.5[MMA]1.0. From the results obtained, the initiation mechanism of vinyl polymerization by the NBS/PTS system was proposed and discussed.