An experimental study has been carried out for a batch PMMA Polymerization reactor in order to establish the validity of the mathematical model previously developed by the present authors and also to investigate the charac-teristics of the polymerization reactor systme. The measured values of the monomer conversion and the molecular weights turned out to be in good agreement with the model prediction throughout the course of reaction. To examine the reactor characteristics systematically we considered three kinds of reactor temperature trajectory-constant, linearly increasing with time and linearly decreasing with time. As the reaction temperature increased or the initial concentra-tion of the initiator increased, the monomer conversion became higher and the average molecular weights of the polymer produced became lower. The polydispersity, however, always tended to increase as the reaction proceeded. Based on the comparison between the experimental results under various reaction conditions and the results of model analysis, it was confirmed that the monomer conversion and the average molecular weights of the polymer could be predicted with reliability.