Semibatch emulsion polymerization of methyl methacrylate (MMA) with neat monomer feed in the presence of sodium lauryl sulphate as emulsifier and potassium persulphate as initiator was investigated. The effects of the monomer feed rate (R-a), the emulsifier concentration, and the monomer distribution ratio between the initial charge and feed on the kinetic features of MMA emulsion polymerization in a semibatch reactor were studied. Under monomer-starved conditions particles did not undergo an appreciable growth during polymerization and as a result a large number of particles were formed. The number of particles increased significantly as R-a decreased. The number of polymer particles formed under starved conditions showed an exponent of - 1.98 against R-a, which is larger than the value of - 0.67 that is theoretically obtained for the styrene monomer. The average molecular weights decreased and the molecular weight distribution became narrower with decreasing R-a. The steady state rate of polymerization (R-pss) was confined to the correlation of the type R-pss approximate to R-a when a high concentration of the emulsifier was used. The rate of polymerization under monomer-starved conditions was found to depend on the size of polymer particles formed. The experimental results suggest that models, which can take account of more specified size-dependent kinetic parameters, should be developed for prediction of kinetic behavior of MMA in semibatch reactors.