Perovskite-like NaTaO3 photocatalyst powders have generally been synthesized with a solid-state method, which formed the orthorhombic phase that has a direct band gap and a Ta-O-Ta bond angle of ca. 163 deg . The present work reports a sol-gel synthesis, in which NaTaO3 nanoparticles were obtained at a temperature as low as 500 deg C by using sodium acetate and tantalum chloride as the starting materials and citric acid as the complexing agent. Because of the low-temperature condition used in the synthesis, the sol-gel NaTaO3 was of the monoclinic phase that has an indirect band gap, high densities of states near the band edges, and a Ta-O-Ta bond angle close to 180 deg . Thanks to the surface area as well as the electronic and crystalline structures, the sol-gel NaTaO3 was considered more favorable to photocatalytic reactions than the solid-state material. This interpretation was supported by the finding that the sol-gel NaTaO3 exhibited a remarkably higher photocatalytic activity in water splitting than the solid-state material.