A BiOI/SnS₂ p–n junction is prepared by depositing BiOI particles on flowerlike SnS₂ flakes. The heterojunction formed between p-type BiOI and n-type SnS₂ brings greatly improved photocatalytic activity compared with pure SnS₂ or BiOI in the degradation of Rhodamine B dye under visible light and sunlight irradiation. The improved photocatalytic performance is explained by the synergetic effects of the formation of a p–n junction between BiOI and SnS₂. The migration of photogenerated carriers can be promoted by the electric field established at the heterojunction interfaces, leading to effective separation of the photogenerated electron–hole pairs and reduced electron–hole recombination. The BiOI/SnS₂ heterojunction will find promising applications in photocatalysis and solar energy conversion.