In this study, Zinc hydroxystannate/tin dioxide/reduced graphene oxide (ZnSn(OH)₆/SnO₂/rGO) ternary nanocomposites were synthesized via a facile one-step hydrothermal route by using graphene oxide, zinc nitrate hexahydrate, and tin (IV) chloride pentahydrate as the precursors. The crystal structure, morphology, and optical properties of ZnSn(OH)₆/SnO₂/rGO ternary nanocomposites were characterized by x-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Raman spectroscopy and UV–vis spectroscopy, respectively. The results of XRD pattern revealed the formation of fcc perovskite ZnSn(OH)₆ (ZHS) and tetragonal SnO₂ structure. The FESEM images displayed that the ZHS microcubes and SnO₂ nanoparticles were distributed on the graphene sheets. The composites were used as photocatalyst for degradation of methylene blue (MB) molecules. The photocatalytic performance of the samples showed that the ZHS/SnO₂/rGO nanocomposite exhibited a much higher photocatalytic activity than pure samples. The ternary nanocomposite synthesized at 160 °C with a graphene oxide concentration of 1 mg/mL has the ability to completely degradation MB in less than 60 min under UV radiation. The rate of hydroxyl radical (·OH) generated in the photocatalytic process was investigated using PL spectroscopy and coumarin (COU) as a probe molecule. Thus it can be intended that the mechanism of MB degradation by the as-synthesized nanocomposites followed indirect oxidation of the dye by ·OH generated during the photocatalyst process.