In this paper, the effects of cerium content on the structural and electrochemical properties of the La0.8-xCexMg0.2Ni3.5 (x=0, 0.05, 0.10, 0.15, 0.20) hydrogen storage alloys have been studied systematically. XRD analyses show that all these alloys consist of hexagonal Ce2Ni7-type main-phase, hexagonal CaCu5-type phase, and rhombohedral PuNi3-type phase. The P-C isotherms curves show that the plateau pressure of the hydrogen desorption increases gradually and the plateau region becomes narrower with increasing the Ce content in the alloys. It is also found that with increasing the Ce content, the discharge capacity at 303 K decreases and the cycling life can be gradually improved, but the discharge capacity at 233 K increases firstly and then decreases. The high rate dischargeability (HRD) and the exchange current density I0 increase but the hydrogen diffusion coefficient D of the alloy electrodes decreases with the increase of Ce content at 233 K. These imply that the charge-transfer reaction on the surface of alloy electrodes is the rate-determining step at 233 K