Photocatalytic degradation of aqueous cyanide with modified TiO2 was studied. The change of pH of the suspension with P25, a well known photocatalyst, was monitored. The initial pH of the suspension was around 10.5 and was observed to decrease continuously up to 9 as the reaction goes on. P25 was impregnated with heteropoly compounds in the hope of enhancing the activity of P25. Phosphomolybdic acid (PMA) and phosphotungstic acid (PTA) were chosen as the enhancing materials. In the case of PMA/TiO2, the activities were shown to be similar to that of pure P25. While, in the case of PTA/TiO2, the activities were better than that of P25 over the range of loading amounts of PTA adopted in this study. Especially, 3 wt% PTA/TiO2 showed the best activity of 86% of the conversion of cyanide. The obvious enhancement of the activity ded not result from the enhancement of adsorption property of the catalyst. Moreover, the activity enahncement was not ascribed to both P25 modified during hydrothermal treatment and PTA eluted from the catalyst during the reaction. Therefore, the enhancement of the activity was thought to be largely due to the increase of the photocatalytic activity itself of the catalyst.