In this study, we report a novel carbon-based semiconductor photocatalyst g-C3N4/ZnWO4 nanocomposites with various contents of ZnWO4 were successfully constructed through a facile and eco-friendly in situ hydrothermal synthesis. The structure, morphology and chemical states of the as-prepared nanocomposites were studied by XRD, TEM and XPS measurements. Further, the surface of the fabricated 2D g-C3N4 nanosheets was completely decorated with 1D ZnWO4 nanorods. The results of photocatalytic investigations signify that the synthesized heterostructured g-C3N4/ZnWO4 photocatalysts display substantially improved catalytic performance for the decolorization of rhodamine B (RhB) upon visible-light treatment. The improved catalytic activity could be attributed to the formation of heterojunction between g-C3N4 and ZnWO4, and effective photogenerated electron-hole pair's separation. A likely catalytic reaction mechanism for the improved decomposition efficiency of RhB by g-C3N4/ZnWO4 nanocomposites is also proposed.