Abstract: Photopolymerization of methyl methacrylate (MMA) has been studied kinetically using several organic disulfides as photoinitiator. Experimental results show that the structural effect of disul’fides on polymerization rate Rp is quite obvious. The initiation activities of various disulfides may be arranged in following order (P-CH₃C₆S)₂ > (t-C₄H₉S)₂>(C₆H₅CH₂S)₂, (n-C₁₂H₂₅S)₂ and ((C₂H₅)₂NC₂H₄S)₂. The initiation efficiency of di-toluene disulfide (DMDS)can bear comparison with benzoin ethers. The RP was found to depend highly on the nature of solvents and is proportional to [MMA] and [DMDS]^0.1(N₂) or [DMDS]^0.2(O₂). The singlet and triplet energy of DMDS have been determined to be E_s72.2kcal/mol and E_T57.3kcal/mol, respectively, which considerably lower than that of conventional vinyl monomers.It indicates that DMDS is qualified as photoinitiator for vinyl polymerization. From the results obtained the initiation mechanism of polymerization is proposed and discussed.