The electrochemical performance of mesoporous carbon (C)/tin (Sn) anodes in Na-ion and Li-ion batteries is systematically investigated. The mesoporous C/Sn anodes in a Na-ion battery shows similar cycling stability but lower capacity and poorer rate capability than that in a Li-ion battery. The desodiation potentials of Sn anodes are approximately 0.21 V lower than delithiation potentials. The low capacity and poor rate capability of C/Sn anode in Na-ion batteries is mainly due to the large Na-ion size, resulting in slow Na-ion diffusion and large volume change of porous C/Sn composite anode during alloy/dealloy reactions. Understanding of the reaction mechanism between Sn and Na ions will provide insight towards exploring and designing new alloy-based anode materials for Na-ion batteries.