The characteristics and mechanisms of enhanced electrochemical properties of Ti0.4V0.3Mn0.15Cr0.15 + x wt % LaNi3.55Co0.75Mn0.4Al0.3 composite alloys produced by ballmilling were investigated. Surface modification of Ti0.4V0.3Mn0.15Cr0.15 alloy by ballmilling with LaNi3.55Co0.75Mn0.4Al0.3 can significantly improve its electrochemical properties. After 30 min of ballmilling, the discharge capacity increases from 205 mAh g(-1) for the plain Ti0.4V0.3Mn0.15Cr0.15 alloy to 420 mAh g(-1) for the Ti0.4V0.3Mn0.15Cr0.15 1 50 wt % LaNi3.55Co0.75Mn0.4Al0.3 composite alloy. The improvement of cycle life and high-rate dischargeability of the composite alloy may be attributed to good catalytic ability of the LaNi3.55Co0.75Mn0.4Al0.3 alloy, which not only provides the alloy with electrochemical activity, but also hinders the formation of oxide film and decreases the dissolution of V into KOH electrolyte. (C) 2004 The Electrochemical Society.