Five-member cyclic dithiocarbonates were synthesized by the reactions of carbon disulfide with benzoic, p-anisic, p-chlorobenzoic, 1-naphthalenecarboxylic, pnitrobenzoic, and p-(tert-butyl)benzoic glycidyl esters, and their cationic ring-opening polymerizations were carried out with methyl trifluoromethane sulfonate and trifluoromethane sulfonic acid as initiators at room temperature to 80°C. Polymers with number-average molecular weights of 3400 -24,900 were obtained in high yields, and their structures were estimated by NMR and IR spectroscopy. The monomers showed a clear difference in the polymerization rate according to the substituents. The rate of polymerization decreased in the order of p-chlorobenzoic Ն benzoic Ͼ 1-naphthalenecarboxylic Ͼ p-nitro-benzoic Ͼ p-tert-butylbenzoic Ͼ p-anisic. The data of the reaction kinetics, NMR studies, and molecular orbital calculations proved a plausible mechanism involving the participation of p-substituted benzoyloxymethyl groups to stabilize the cationic propagating end. The polymers showed decomposition temperatures with 5% weight loss ranging from 200 to 260°C. No glass-transition temperatures for the polymers were observed below 200°C by differential scanning calorimetry.