The La(0.7)Mg(0.25)Ti(0.05)Ni(2.975)Co(0.525) (AB(3)) alloy was modified with different contents of polyaniline (PANI) through ball milling. XRD, SEM and FTIR were used to characterize the properties of the AB(3)/x PANT composites (x=1, 2, 3 and 4wt%). The effects of PANI on the electrochemical properties of AB(3) alloy electrode were studied by charge-discharge, electrochemical impedance spectroscopy (EIS), linear polarization (LP) and potentiostatic discharge experiments. The XRD, SEM and FTIR results showed that ball milling did not change the characterizations of PANT and AB(3) alloy but decreased the average particle size of AB(3) alloy. The charge-discharge results indicated that the maximum discharge capacity of AB(3) alloy electrode decreased with the addition of PANT. However, the discharge cycle stability of AB(3)/PANI composite electrodes increased firstly and then decreased with the increase in PANT content. The EIS and LP curves showed the same trends with the discharge cycle stability. The hydrogen diffusion coefficients of AB(3)/PANI composites were estimated from the potentiostatic discharge curves, indicated the opposite trend with the discharge cycle stability. When the PANT content was equal to 3 wt%, the AB(3)/PANI composite electrode exhibited an optimal electrochemical kinetic property. (c) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.