Body-centered-cubic type CuPd nanoalloys were synthesized by a chemical reduction method. Photocatalytic hydrogen evolution and nitrate reduction were simultaneously examined over CuPd nanoalloys deposited on TiO2 (CuPd/TiO2). The efficiency of hydrogen evolution over CuPd/TiO2 was better than that over Pd/TiO2. As for nitrate reduction, ammonia was selectively (78%) produced with hydrogen generated photocatalytically over CuPd/TiO2. The continuous generation of nascent hydrogen atoms on the surface of the CuPd nanoalloy, where Cu and Pd are homogeneously mixed, led to the high selectivity for ammonia.