In this paper, the effects of platinum addition on the structure and electrochemical properties of MgNiPt (Pt = 1.0, 2.0 and 3.0 at.%) metal hydride alloys are discussed. The ternary alloys were processed by mechanical alloying and had their structures characterized by X-ray diffraction, transmission electron microscopy and in situ X-ray absorption spectroscopy. It is observed that the structure of the alloys is formed by amorphous and nanocrystalline phases, with the size of the nano-grains close to 5 nm. The electrochemical properties were evaluated by galvanostatic charge and discharge cycles using different discharge rates in the range of 10-80 mA g(-1). The best result was obtained for the Mg49.0Ni49.0Pt2.0 alloy, which showed smaller decay of the discharge capacity as a function of the charge/discharge cycle number, retaining 64% of its initial discharge capacity (364 mAh g(-1)) after 10 cycles. (c) 2006 Elsevier B.V. All rights reserved.