It was shown that the polymerization rate of propylene sulfide is second order with respect to monomer concentration and half order with respect to catalyst concentration. A mechanism of himolecular coordinated propagation of propylene sulfide and association of the catalyst in the polymerization system was proposed. The activation energy of polymerization was measured as 12.2 ± 0.5 kcal/mole. Chain transfer constanst to monomer and solvent were calculated. The change of molecular weight and molecular weight distrbution with conversion was followed by GPC which was improved by ad-ding LiCl to eluant.