A new type of solid superacid (SO42-/TiO2/Nd3+) was used for the ring-opening polymerization of chloromethylthiirane (CMT). TiO2 . H2O immersed in a sulfuric acid solution containing Nd3+ ions and calcined at 600 degrees C gave the solid superacid for initiating the polymerization of CMT. The effects of polymerization temperature and amount of the initiator on the CMT polymerization were studied. Poly(CMT) obtained has higher molecular weight ((M) over bar(W) = 52000) than ever reported.