The decomposition of C6H5CI, which is similar to harmful compounds such as PCBs, was investigated using the basic molten salt mixtures, KOH- K2CO3 and NaOH-Na2CO 3. A sample of C6H5Cl was injected, together with a carrier gas, either imitation air (N2-21%O2) or N2, into the molten salts in the temperature range from liquidus to 700°C The exhaust was analyzed by using GC/MS both quantitatively and qualitatively. The concentration of C6H5Cl remaining in the exhaust was extremely low and the decomposition efficiency was at least 99.999% for both imitation air and N2 as carrier gas. However, C 6H5Cl was not completely decomposed to CO2 and H2O if the concentration of oxygen was lower than the stoichiometric ratio: instead many intermediate compounds were formed, and all were chlorine-free. The results indicated that the chlorine in C6H 5Cl was effectively removed by the alkali hydroxide-carbonate mixtures even if oxygen is not contained in the carrier gas. Potassium salts are somewhat better than the sodium salts in their capacity for decomposition.