The effects of n-butyl chloride，i-propyl chloride，t—butyl chloride，chloroform，carbon tetrachloride，methylene chloride，benzyl chloride， chlorobenzene and titanium tetra-chloride on the stereospecific polymerization of butadiene catalyzed by triisobutyl alu-minum and titanium tetraiodide have been studied．n-Butyl chloride or i-propyl chloride induces gel-formation during the polymerization．t-Butyl chloride or benzyl chloride in- hibits the polymerization，when，its quantity added is larger than the excess moles of triisobutyl aluminum． Both chloroform and carbon tetrachloride can lower the molecular weight of the polymer formed，but the latter does so more seriously and at the same time lowers the conversion of the polymer．Titanium tetrachloride also reduces the mole-cular weight of the polymer，but meanwhile changes the structure of the polymer．Neither methylene chloride nor chlorobenzene exerts any effect on the stereospecific polymeriza-tion of butadiene． In order tO explain the above phenomena，the reaction between tri-isobutyl aluminum and the chlorine-containing compounds has been studied．It has been observed that benzyl chloride or t-butyl chloride reacts with triisobutyl aluminum in-stantaniously，forming chloride ion equivalent tO the chlorine atom present in the com-pound，while chlorobenzene or methylene chloride reacts only very slightly． n-Butyl chloride or i-propyl chloride reacts with triisobutyl aluminum violently after an induction period，forming a large quantity of chloride ion．It has been shown that the gel-formation induced by n-butyl chloride during the polymerization is due to the concurrent cationic polymerization catalyzed by the aluminum chloride formed between the excess triisobutyl aluminum and the n-butyl chloridc after ao induction period．