In order to investigate the effects of an external electron donor on catalyst active sites in propylene polymerization, physical properties of the produced polymers are measured with various techniques. From the thermal analysis and gel permeation chromatography( GPC) measurement, it is found that an external electron donor transfers the catalyst active sites from atactic sites via low isospecific sites to high isospecific sites. There are some differences between gas and slurry phase reactions. This may be due to the differences in diffusion phenomena with polymerization types. Polymer crystalline formations, such as spherulite and lamella structure, are observed by an image analyzer and closely coincide with the GPC results in molecular weight of polypropylene. From the results of ultraviolet visible (UV VIS) and Fourier transform infrared (FTIR) experiments, it is found that some complexes are formed between cocatalyst and the external electron donor, and it is supposed that those complexes are strongly associated with catalyst active site transition.