Polymerization of methyl methacrylate was studied with a cobalt acetylacetonate -diethyl zinc catalyst initiator system in benzene medium at 40 degrees C. When the stoichiometric ratio of Zn/Co is 2, the activity for polymerization is found to be maximum. The structure of the obtained polymethyl methacrylate is compared with that obtained using a free-radical initiator such as benzoyl peroxide. The structure of polymer and the (M) over bar(w)/(M) over bar(n) values indicate that cobalt acetylacetonate-zinc diethyl system has pronounced free-radical characteristics. A suitable mechanism is proposed from the kinetic studies.