In this paper, we report a simple hydrothermal method for preparation of ultrathin carbon-coated CdS (CdS@C) nanobelts. The CdS@C nanobelts show superior electrochemical properties as an anode material for Li-ion batteries. The optimized CdS@C composites deliver a reversible capacity around 910 mAhg-1 and 48 mAhg-1 at 0.1 Ag-1 and 30.0 Ag-1, respectively. Moreover, the optimized nanobelts are also potential materials for Na storage. A stable capacity around 240 mAhg-1 is obtained at 0.1 Ag-1, even after 100 cycles.