A photocatalyst which has high catalytic activity, is nontoxic, has a long life, can utilize visible light as it is for photocatalytic reactions, and is useful especially for hydrogen generation; and a process for producing the same. The photocatalyst comprises cadmium sulfide, has a capsule structure, wherein platinum is supported thereto. It can be obtainable by bubbling H.sub.2S gas into a liquid to which particles of cadmium oxide have been added.