SiO₂/Mg(OEt)₂/ethyl benzoate/TiCl₄ catalysts need for propylene polymerization were prepared by using silica(Davison-952) as a support, which is known to produce polypropylene with spherical shape and narrow particle size distribution. Propylene polymerization was carried out with the silica supported catalyst cocatalyzed with triethylaluminum(TEA) in the presence of an external electron donor(EED), p-ethoxy ethyl benzoate(PEEB) at 8atm. The effect of TEA, PEEB concentration and polymerization temperature on activity as well as stereospecificity was investigated. The maximum average polymerization rate during the initial first hour of polymerization was obtained at the mole ratio of [TEA]/[Ti]=200 and 70℃. The increase of TEA concentration decreased stereospecificity. As the polvmerization temperature increased, the stereo-specificity did not change. The polymerization activity in the absence of PEEB was 16.2kg-PP/g Ti-hrㆍatm and the isotactic indox was 84% at the molar ratio of TEA to Ti of 200 and 70℃. However, the activity decreased to 12.4kg-PP/g-Tiㆍhrㆍatm and isotactic index increased to 93% at the same polymerization condi-tion except for the addition of PEEB of which amount is 17% of [TEA]. Further addition of PEEB([PEEB]/[Al]=0.25) decreased the activity to 5.2kg-PP/g-Tiㆍhrㆍatm and increased isotactic index to 96%.