A generator-column technique was used to prepare aqueous solutions of PCBs. The degradation of 2-chlorobiphenyl, Aroclor 1248, Aroclor mixture (1221, 1016, 1254, and 1260) and St. Lawrence River water by simulated sunlight or sunlight has been investigated in the presence of aqueous suspensions of TiO2. The effect of TiO2 concentration and pH on the degradation rate of PCBs have been studied. The reaction rate followed apparent first-order kinetics and increased with increasing TiO2 concentration. The half-life of the degradation process for 2-chlorobiphenyl is 20 minutes at pH 10 and 9 minutes at pH 3 in the presence of 25 mg/L of TiO2. Less chlorinated PCBs decomposed faster than higher chlorinated ones. The rate constants and half-lives of individual PCBs in the commercial PCB mixture and St. Lawrence River water were also measured.