The effect of LiClO4 on the polymerization of methyl methacrylate (MMA) with dimethyl 2,2’-azobisisobutyrate (MAIB) was investigated at 50 degrees C in methyl ethyl ketone. The polymerization proceeded homogeneously even at [LiClO4] as high as 3.00 mol/L. The polymerization rate (R(p)) and the molecular weight of the resulting polymer profoundly increased with increasing [LiClO4]. R(p) at 3.00 mol/L [LiClO4] was 12 times that in the absence of LiClO4. The rate equation depended on the presence or absence of LiClO4 : R(p) = K[MAIB](0.5) [MMA](1.5) in the presence of 3.00 mol/L [LiClO4] and R(p) = k’[MAIB](0.5) [MMA](1.0) in the absence of LiClO4. The overall activation energies of polymerization were 38.5 kJ/mol in the presence of 3.00 mol/L [LiClO4] and 77.4 kJ/mol in the absence of LiClO4, respectively. The tacticities of resulting poly(MMA) were insensitive to the presence of LiClO4. In the copolymerization of MMA and styrene, Q and e values of MMA increased with increasing [LiClO4], leading to enhanced alternating copolymerizability.