Catalytic deactivation in gas phase propylene polymerization with CSBR was investigated in two concepts of chemical and physical ways. In kinetic consideration, catalyst deactivation followed the 2nd order reaction due to chemical phenomenon like active site reduction. In case of physical consideration, catalyst deactivation was progressed by monomer diffusion resistance. It was due to formation of dense IPP around catalyst at the beginning of polymerization. There were excessive monomer concentration differences between catalyst and polymer surfaces until 90 min after initial polymerization. Consequently, the main reason of catalyst deactivation is not only chemical phenomenon, but also physical one such as monomer diffusion resistance.