Photocatalytic decomposition of halocarbons by using TiO2 and a germicidal lamp was studied for the purpose of developing a treatment process to convert halocarbons into harmless substances. The decomposition rates of chlorodifluoromethane (HCFC-22), carbon tetrachloride and methane were analyzed, because these compounds have the same structure but different constituents. As a result, the decomposition rate was found to be highest for HCFC-22, followed by methane and CCl4 in that order and reactions were first-order within the concentration range used. The activation energies obtained from the overall reaction rate constants were 13.7 kJ . mol(-1) lor HCFC-22, 66.1 kJ . mol(-1) for CCl4 and 16.6 kJ . mol(-1) for methane.