Nanocrystalline LaMg12-Ni composites containing carbon nanotubes (CNTs) were prepared by two ball-milling ways, and the resulting microstructure and electrochemical characteristics were investigated. It is found that the discharge capacities and high-rate dischargeabilities (HRDs) of the CNT-containing composites prepared by ball-milling as-prepared nanocrystalline LaMg12-Ni composite and CNTs for 1 h (denoted as Composite-CNT1-1) were obviously higher than that by ball-milling LaMg12 alloy, Ni powder and CNT1 together for 12 h (denoted as Composite-CNT1-2). The highest discharge capacity reaches 999.8 mA h/g. Raman spectra and X-ray diffraction (XRD) patterns show that the structure of the CNTs still exists and the defect increases in Composite-CNT1-1. However, in Composite-CNT1-2, due to the overlong ball-milling time, the crystalline structure of the CNTs has been destroyed and amorphous carbons have formed. Cyclic voltammetry and electrochemical impedance spectra measurements indicate that the CNT modification in Composite-CNTI-1 increases the electrocatalytic activity and surface area, which leads to its higher discharge capacity and HRD. The larger electrochemical reaction resistance caused by amorphous carbon in Composite-CNT1-2 results in its lower discharge capacity and HRD. The CNT modification has negligible effect on the diffusion process of hydrogen from the surface to the bulk of the composites. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.