Detoxification of polychlorinated biphenyls (PCBs) is accelerating globally. when PCBs in alkaline 2-propanol are irradiated with ultraviolet (UV) rays, they are reduced to biphenyl, and sodium chloride (NaCl), acetone and H2O are generated as by-products. But in UV irradiating process, when dechlorination of PCB progresses, PCB decomposition rate is reduced because of biphenyl decomposition and generating many derivatives. Therefore, we have developed a hybrid method using UV-irradiation and a noble-metal catalyst which can dechlorinate PCBs in the presence of biphenyl. By this method, the concentration of PCBs is decreased below 10 ppb, and both NaCl and biphenyl can be recovered as by-products. In addition, the UV/Catalyst method is environmentally sound, because organic chlorine compounds such as PCDDs, PCDFs, Co-PCBs and OH-PCBs are decomposed to below detectable level.