Carbon tetrachloride can be decomposed to sodium chloride, water and carbon dioxide in supercritical water containing sodium hydroxide following the reaction path shown in Fig. 1. Fig. 2 shows the flow diagram of this reaction system. Carbon tetrachloride and sodium hydroxide aqueous solutions are pumped respectively into reaction coil for decomposition, and then the reaction product is collected in a glass tube placed downstream of the back-pressure regulator (5) as shown in Fig. 2. Decomposition efficiency at each reaction temperature was calculated by measuring the amount of sodium chloride (chloride ion) by ion-chromatography (see Fig. 3) and the amount of remaining carbon tetrachloride by gas chromatography (see Fig. 4), respectively.