Photocatalytic degradation of aqueous cyanide with heteropolytungstate-modified TiO2 was studied. A Keggin-type tungstophosphate, PW12O40(3-) was chosen as an enhancing material. The modified TiO2, named HPT/P25, was prepared by impregnation of P25, a well known photocatalyst, with the heteropoly compound. The change of pH of the suspension with HPT/P25 was monitored. The initial pH of the suspension was around 10.5 and was observed to decrease continuously up to 8.5 which changed to 9 in the case of P25 as the reaction went on. Polyoxometalates usually turn blue with a broad intense absorption at around 700 nm. In the case of HPT/P25, however, the color change did not happen during the reaction suggesting that the reoxidation step was much faster than the reduction step presumably due to adjacent oxygen species adsorbed on the surface of TiO2. In the case of 1 wt% HPT/P25, the activity increased as calcination temperature was raised in the range of 110 ℃ through 200 ℃. Beyond 200 ℃, the activity was saturated at about 50% of cyanide conversion up to 300 ℃. And, in the case of 30 wt% HPT/P25, almost the same pattern was observed as that of 1 wt% HPT/P25. This tendency was thought to be strongly related to the Keggin structure of the heteropolytungstate in the catalysts.