A number of TiCl4 catalysts supported on MgCl2 which was activated by the recrystallization method using different alcohols were prepared with ethyl benzoate or dibutyl phthalate as the internal electron donor. All the catalysts were characterized by BET, x-ray diffraction, and hydrolysis-GC analysis. Kinetics of polymerization of 1-octene was studied with three of the above catalysts (having different internal electron donors) activated by AlEt3. The rate of polymerization increased linearly with increasing temperature, and catalyst and monomer concentrations. From the Arrhenius plot, the overall activation energies of polymerization were determined and the dependence of rate on the AlEt3 concentration could be explained by the Langmuir-Hinshelwood mechanism. C-13-NMR was used to study the effect of internal electron donors on the % isotacticity of poly(1-octene). The catalytic activities of all the catalysts were compared in 1-octene polymerization.