In this paper, the effects of substitution of Pr for La on the microstructure and electrochemical properties of La0.7-xPrxMg0.3Ni2.45Co0.75 Mn0.1Al0.2 (x = 0.00-0.30) hydrogen storage alloys have been studied systematically. XRD Rietveld analyses showed that all alloys consisted of (La, Mg)Ni-3 phase and LaNi5 phase. With the increase in Pr content, the lattice parameters and cell volumes of the component phases all decreased. The electrochemical studies showed that the maximum discharge capacity decreased from 366 to 346 mAh/g when x increased from 0.00 to 0.30. However, the cycling stability of the alloy electrodes was improved with the increase in Pr content. Moreover, the high rate dischargeability, the exchange current density 10, the limiting current density I-L and the hydrogen diffusion coefficient D of the alloy electrodes all increased first then decreased with increasing x, reaching an extreme when x is 0. 15, which indicated that the alloys' kinetics of hydriding/dehydriding increased first up to x = 0. 15 and then decreased with further increasing x to x = 0.30. (c) 2007 Published by Elsevier Ltd on behalf of the International Association for Hydrogen Energy.