V-based TiV 2 . 1 Ni 0 . 3 alloy with high hydrogen storage capacity was surface-modified by ball-milling with amorphous MgNi alloy prepared by mechanical alloying. In charge-discharge cycle measurements, the decrease in discharge capacity for the prepared TiV 2 . 1 Ni 0 . 3 -MgNi composites was effectively suppressed in comparison with the TiV 2 . 1 Ni 0 . 3 alloy. In particular, ball-milling for 3 h is the most effective in the present study. This was explained by surface analyses with EPMA mapping and X-ray photoelectron spectroscopy (XPS). Changes in the EPMA maps, XPS spectra and depth profiles of the surface alloy components suggested that the ball-milling caused the mutual diffusion between Mg and a little of the Ni components in the MgNi alloy and Ti and V components in the TiV 2 . 1 Ni 0 . 3 alloy at the interface between both alloys. In addition, stable time course of rest potential for the TiV 2 . 1 Ni 0 . 3 -MgNi composite electrodes immersed in 6 M KOH solution also showed the effectiveness of the surface modification with ball-milling.