A comparative study of hydrodechlorination of carbon tetrachloride and 1,2dichloroethane over supported Pt catalysts showed a large effect of support ( C, Al2O3, SiO2) on the catalytic behavior. High selectivity towards CHCl3 ( from CCl4), similar to 80%, was found for Al2O3- and SiO2-supported Pt. In 1,2-dichloroethane reaction, Pt/Al2O3 appeared more active than the other catalysts but the least selective towards C2H5Cl, giving mainly ethane. Al2O3- and C-supported catalysts contained more chlorine and carbon after hydrodechlorination.