The kinetics of photosensitized polymerization of methyl methacrylate with benzoin was investigated. The rate of polymerization was proportional to the square root of the concentration of benzoin and the first power of the monomer. The equation Rp=K1 ([M]‐α1) ([B]0.5+α2) was proposed, and K1 α1 and α2 were evaluated as 0.999×10−4, 0.181 and 1.11×10−2, respectively. The rate of polymerization was also proportional to the square root of light intensity in accordance with the equation Rp=5.65×10−12 I0.5. Carbon tetrachloride and chloroform markedly decreased the average degree of polymerization. The chain transfer coefficients were evaluated as 2.44 × 10−3 and 1.90 × 10−3 for carbon tetrachloride and chloroform respectively. Copyright © 1969 The Chemical Society Located in Taipei & Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim, Germany