β,β-Dideuterated poly(viny1 chloride) (β,β -d2-PVC) was chlorinated under conditions of photochemical suspension chlorination in concentrated hydrochloric acid with addition of chloroform as a swelling agent, and also under conditions of thermal solution chlorination in tetrachloroethane. The1H-NMR spectra of chlorinated β,β -d2PVC (β,β -d2CPVC) were measured. The deuterium concentration was determined in combustion products of β,β -d2CPVC as the D2O:H2O ratio by means of mass spectroscopy. It was found that the concentration of CHC1- groups decreases in both the photochemical suspension chlorination and in the thermal solution chlorination. The structural nonidentity of β,β -d2PVC chlorinated in suspension and in solution was confirmed.