Group-III nitrides are expected to be used in future photocatalytic materials. InGaN is expected to be used for photocatalytic applications in the visible light region. Photocatalytic materials are used primarily in coatings and powders, and powdered photocatalysts are expected to be formed from group-III nitride powders. In this study, we produced GaN powders by nitriding Ga precursors at high temperatures under an atmosphere of NH3. The photocatalytic characteristics of the GaN powder were dependent on nitrization temperature. In addition, the crystallinity of the GaN powders and the photocatalysis were rapidly improved at nitrization temperatures over 1000°C.