The effects of particle size on the electrochemical property of MlNi(3.65)Co(0.75)Mn(0.4)Al(0.2) have been systematically investigated. The results at charge/discharge current of 200 mA g(-1) showed that the smaller the particle size, the larger is the first discharge capacity and the earlier is the saturation capacity reached, however, the saturation discharge capacity increases with the increase in particle size. The particle size dependence of high-rate dischargeability is similar to that of the saturation discharge capacity when the discharge current is less than 600 mA g(-1),but it changes at 600 mA g(-1) or more; the higher the discharge current, the more obviously the particle size affects the property of the alloy. The cycle life test at 300 mA g(-1) showed that the discharge capacity in all 400 cycles increases with the increase of particle size, and the discharge capacity decay rate is almost the same except that the rate for 25.5 um particles is slightly faster.