The kinetics of the polymerization of 4-methylpentcne-1- with the MgC12|EB|Ticl4|Al(iBu)3 catalyst systems have been investigated. The conditions and requirements to achieve the highest activity and stereospecificity of the MgC12-supported catalyst systems were discussed. Moreover, the role of aluminum alkyl and ethyl benzoate on the activity and stereo-regularity of the polymers have been reported.