The effect of propylene (Pr), styrene (St), hexene-1 (He) and cyclopentadiene (Cp) employed in the preactivation of TiCl3 catalyst for propylene polymerization was investigated. The catalyst was synthesized by reduction of TiCl4 in toluene solution with AlEt3.DBE (di-n-butyl ether) complex. Catalyst activity and stereospecificity, soluble polymer content in the polymerization diluent were evaluated. The results show that the prepolymerization altered the catalyst performance and is influenced by the type of monomer employed in the preactivation step.