Refractory organic contaminants have been often reported that come from increasing consumption of organic materials. Lots of researches have been done for comlete mineralization to CO2 and H2O by attack of active radical species, generated on the UV irradiated TiO2 surface. The effect of pH in trichloroethylene(TCE) aqueous solution on the photocatalytic activity of TCE degradation was studied. The pH of the solution was adjusted from 3 to 11 by using HNO3 and NaOH. P25-TiO2 from Degussa has mixed structure of anatase(75%) and rutile(25%) and physical mixture(M-TiO2) of Aldrich TiO2(anatase) and KIER TiO2(rutile) were used. The optimum degradation of TCE appeared when the pH of the aqueous solution was 9 by using Degussa P-25. And photocatalytic activity of Degussa P-25 and M-TiO2 was almost same when the aqueous solution pH was 9.