The effect of CN- as a hole scavenger on the photocatalytic hydrogen evolution from water was investigated over NiO/TiO2. A considerable amount of hydrogen was produced in the presence of CN-; the total amount of hydrogen evolved was proportional to the total amount of CN- ion in the solution. Quantum yield was 0.12 at 25 degreesC and 0.32 at 75 degreesC; the increment of quantum yield was about 0.048 per 10 degreesC increase of the reaction temperature. Nickel cyanide complex, Ni(CN)(4)(2-), was generated from NiO/TiO2 in the presence of CN-. The Ni complex decomposed under UV light in the course of hydrogen evolution, resulting in OCN- formation. In addition to producing valuable hydrogen, this complex decomposition under UV light might be a valuable process to treat wastewater containing harmful cyanide complexes. Heat treatment of NiO/TiO2 catalyst at 700 degreesC was effective for reducing nickel dissolution significantly.