Heterojunction photocatalysts composed of CdIn₂S₄ (CIS) nanocrystals and graphitic carbon nitride (g-C₃N₄) nanosheets (CN) have been synthesized using a simple two-step wet chemistry method. In this system, CN nanosheets not only act as a substrate for the growth and uniform distribution of CIS nanocrystals but also play a key role in the photocatalytic degradation of organic pollutants with high efficiency. The CdIn₂S₄/g-C₃N₄ (CIS/CN) heterojunction photocatalysts exhibited better photocatalytic activity than that of pristine CIS and CN in photocatalytic degradation of both an organic dye (methyl orange) and an antibiotic (tetracycline hydrochloride). The enhanced photocatalytic performance might be ascribed to the formation of a heterojunction structure with strong interface interaction, which is beneficial to the photoinduced charge transfer between CIS and CN and efficient to accelerate the seperation of photogenerated electrons and holes. The as-synthesized heterojunction photocatalysts also showed good photocatalytic stability. After four cycles, the photocatalytic activity almost remains unchanged. The heterojunction photocatalysts with excellent photocatalytic performance and reusability may provide a new sight in the development of a photocatalyst with high efficiency for practical application of water purification.