ZnS nanoparticles embedded in reduced graphene oxide (RGO) were prepared via a facile microwave-assisted method and applied as anode materials of sodium-ion batteries (SIBs). The as-prepared composites exhibit excellent sodium storage properties. A maximum specific capacity of 481 mAh g−1 at the specific current of 100 mA g−1 can be achieved after 50 cycles by optimizing the RGO content in the composites. The improved sodium-ion storage ability can be ascribed to the enhanced specific surface area and increased electric conductivity due to the introduction of RGO and the decreased size of ZnS particles which can shorten the pathway of sodium-ion diffusion and facilitate the reversible Na+ diffusion kinetics.