Reactions of 1-chlorohexadecane and 2-chloronaphthalene in water under sub- and supercritical conditions have been investigated so as to show the possible use of water for the dechlorinations of these organic chlorides. The reactions were carried out at 275 degreesC to 430 degreesC in a small SUS316 batch reactor under nitrogen atmosphere at the molar organic chloride/water ratio of 1/100. Under subcritical temperatures, hydrolysis reactions occurred catalyzed by H+ ions, whereas under supercritical conditions hydrodechlorinations occurred too, in which hydrogens evolved by the reaction of HCl with the metal wall of the reactor participated. The hydrogenation and hydrogenolysis of the primary reaction products also occurred for 1-chlorohexadecane under supercritical conditions. The dechlorination selectivity was nearly 100% for these organic chlorides irrespective of the reaction conditions employed.