Nanocomposites of NiS2 with graphitic carbon nitride (NiS2/g-C3N4) have been successfully synthesized by means of a facile hydrothermal method. The photocatalytic activities of as-prepared samples were evaluated by monitoring the photodecomposition of rhodamine B under visible light irradiation. The experimental results indicated that visible light-driven NiS2/g-C3N4 composites exhibited an enhanced photocatalytic activity compared to that of pure NiS2, due to the fast generation, separation and transportation of the photogenerated carriers resulting from the addition of NiS2 nanoparticles (NPs). Interestingly, different amounts of NiS2 deposition can affect the photocatalytic activities of the NiS2/g-C3N4 composites. A suitable loading amount of NiS2 NPs presents the best photodegradation performance. The photocatalytic reaction mechanism for the improved photocatalytic performance of NiS2/g-C3N4 catalyst was proposed which was supported by PL, PEC, EIS and active species trapping results. A promising strategy presented here provides a facile route towards the development of economical, noble metal-free composites as photocatalysts for the applications in environmental remediation.