Calcium tantalum oxynitride [Ca2Ta3O9.7N0.2](-) nanosheets were prepared by exfoliating a layered perovskite oxynitride (CsCa2Ta3O9.7N0.2) via proton exchange and two-step intercalation of ethylamine and tetrabutylammonium ions. Monolayer nanosheet was prepared by the above processes, although some bilayer or trilayer nanosheets were also produced. The [Ca2Ta3O9.7O0.2](-) nanosheets exhibited photocatalytic activity for H-2 evolution from water under visible light irradiation. In contrast, CsCa2Ta3O9.7N0.2 exhibited very low photocatalytic activity for H-2 evolution under the visible light irradiation, even when methanol was added to water as a sacrificial agent. The improved photocatalytic activity originates from the characteristics of nanosheets such as their molecular thickness and large surface area. Further, the Rh-loaded [Ca2Ta3O9.7N0.2](-) nanosheets restacked with protons exhibited photocatalytic activity for H-2 and O-2 evolution from pure water under UV-light irradiation. The ratio of H-2/O-2 evolved was around 3. The ratio of N/O in the catalyst remained the same after the photocatalytic reaction, signifying that there was no decomposition of the catalyst during the reaction. This indicates that the present N-doped nanosheet is stable in the photocatalytic reaction.