The effect of AlEt(3) modified by tributylamine (TEA), 1,4-diazabicyclo [2.2.2]octan (DO), 2,2,6,6-tetramethylpiperidine (TMPip), 2,6-dibutyl-4-methylphenol (BHT) and 2-tert-butyl-4-metoxyphenol (TEMP) on the propylene polymerization was studied using a catalyst based on TiCl3 modified with di-n-butyl ether as internal base. The influence of these hindered Lewis bases on the isotacticity, catalyst activity, molecular weight (($) over bar Mn) and molecular weight distribution (MWD) was investigated. It was verified that the Lewis bases modified the percentage of mm triad whereas no significant effect on I.I. was found.