The effects of particle size on the electrochemical properties of the Ml(NiCoMnTi)5 hydrogen storage alloy have been systematically investigated. The results show that the smaller the particle size, the higher the discharge capacity and the better the high -rate-dischargeability and the cycling stability. If two types of powder with different particle sizes are mixed, the smaller the particle size ratio (the average particle size of small component to that of the large one), the higher the discharge capacity. At a mixing weight ratio (the weight of large component to that of the small one) of 7: 3, the highest discharge capacity is obtained.