A hybrid structure involving efficient plentiful ultrasmall SnS2 nanocrystals decorated on flexible reduced graphene oxide (RGO) has been successfully realized via a simple refluxing method. Compared to previous studies, the ultrasmall SnS2 nanocrystals can compactly and orderly cover the RGO nanosheets, increasing the loading number of SnS2 per unit area of the RGO substrates. The ultrasmall SnS2 nanocrystals@RGO nanocomposites were investigated as electrode materials for lithium-ion batteries. In this hybrid structure, RGO was not only used as a solid support to uniformly distribute the SnS2 nanocrystals, but also as a carrier to accelerate electron transport. In addition, the uniform size and homogeneous SnS2 nanocrystals on the RGO nanosheets reduced electrode polarization, resulting in excellent electrochemical performance for lithium-ion batteries. A specific capacity up to 1034 mA h g−1 was realized from an ultrasmall SnS2 nanocrystals@RGO electrode even after 200 cycles at 0.1 C. Importantly, the ultrasmall SnS2 nanocrystals@RGO electrode showed excellent capacity retention for up to 450 cycles even at a high rate of 5 C. The cost-effective synthesis of SnS2 nanocrystals@RGO and excellent electrochemical performance indicates the great potential for this type of nanocomposites as an active electrode for lithium-ion batteries.