Poly(vinyl chloride) with relatively low molecular weight (LMW-PVC) was prepared by suspension polymerization in the presence of some chain-transfer agents, such as mercapto compounds. It is elucidated by means of thermogravimetry, dehydrochlorination, color difference, and discoloration that the resultant LMW-PVC has good thermal stability. The degree of dehydrochlorination of the LMW-PVC obtained by using n-dodecylmercaptan increases with increasing the content of component from the chain-transfer agent. It is found that the LMW-PVC obtained by using mercapto compounds shows better thermal stability (discoloration property) than does the one obtained without using these agents, at the same weight-average polymerization degree.