Metal sulfides have received tremendous attention due to their superior electrochemical performance. In this study, it is the first time that the ternary tin selenium sulfide, SnSe0.5S0.5, is investigated as a potential high-performance anode material for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). The SnSe0.5S0.5/C nanocomposites have also been synthesized through a facile polyol-method followed by a simple hydrothermal process and subsequent sintering. The material demonstrated a high specific capacity and a long-term cycling stability in both Li-ion and Na-ion batteries (625mAhg−1 for LIB at 500mAg−1 rate after 1000 cycles, 430mAhg−1 in a SIB at 200mAg−1 rate after 100 cycles). Furthermore, the kinetic analysis of Li-ions and Na-ions storage revealed that the extrinsic pseudocapacitive contribution could improve the charge transfer rate during the insertion and extraction of Li-ion and Na-ion, thus enhancing the rate performance and cycling stability. These results demonstrated that the novel tin selenium sulfide (SnSe0.5S0.5) material could potentially be an excellent anode material for Li-ion storage and Na-ion storage.