Polymerization of methyl methacrylate (MMA) was carried out in aqueous sulfuric acid medium at 3OoC using ammonium ceric sulfate (ACS)/methyl ethyl ketone ( M E K ) and ammonium ceric sulfate/acetone as redox initiator systems. A short induction period was observed with both the initiator systems, as well as the attainment of limiting conversion for polymerization reactions. T h e rate of ceric ion consumption, Rc,, was first order with respect to Ce(1V) concentration in the concentration range (0.5-5.5) X 10-3M, and 0.5 order with respect to reducing agent concentration in the concentration ranges (0.0480-0.2967M) and (0.05-0.3912M) for Ce(1V)-MEK and Ce(1V)-acetone initiator systems, respectively. A fall in Rce was observed a t higher reducing agent concentrations. T h e plots of Rc, versus reducing agent concentrations raised t o the half power yielded straight lines passing through the origin, indicating the absence of complex formation between reducing agents and Ce(1V). T h e addition of sodium sulfate t o maintain constant sulfate ion concentration in the reaction medium could bring down the Rce values in the present reaction systems. T h e rate of polymerization of MMA, R,, increased with increase in Ce(IV), reducing agent, and monomer concentrations for the Ce(1V)-MEK initiator. T h e rate of polymerization of MMA is independent of Ce(1V) concentration a n d increased with a n increase in reducing agent and monomer concentrations for the Ce(1V)-acetone initiator. At higher concentrations of reducing agent (0.4-0.5M), a steep fall in R, values was observed with both the initiator systems. T h e orders with respect t o Ce(IV), MEK, and MMA using the Ce(1V)-MEK initiator were found t o be 0.23, 0.2, a n d 1.29, respectively. T h e orders with respect to Ce(IV), acetone, and MMA using the Ce(1V)-acetone initiator were found t o be zero, 0.42, and 1.64, respectively. Maintaining constant [SO:-] in the reaction medium could bring down Rp values for the Ce(1V)-MEK initiator system. On the other hand, a rise in Rp values with a n increase in [Na,SO,] could be observed when constant [SO:-] was maintained in the reaction medium for the Ce(1V)-acetone initiator system. A kinetic scheme involving direct attack of Ce(1V) on reducing agent, production of radicals, initiation, propagation, a n d termination of the polymeric radicals by bimolecular interaction is proposed. An oxidative termination of primary radicals by Ce(1V) is also included.