Surface-treated MmNi3.55Co0.75Mn0.4Al0.3 alloy as negative electrode material of nickel-metal hydride battery was employed to improve the high-rate dischargeability. Surface treatment was realized by dipping and stirring the alloy into a HCI aqueous solution with various concentrations at room temperature. The microstructure of the alloy before and after surface treatment was analyzed by X-ray dif-fraction (XRD) and scanning electron microscopy (SEM). The electrochemical properties before and after surface treatment were compared, and the alloy treated in 0.025 mol/L HCI solution showed the optimal high-rate dischargeability.