La0.7Mg0.3Ni3.4-xCo0.6Mnx (x=0.0-0.5) hydrogen storage alloys are mainly consisted of the (La, Mg)Ni3 phase and the LaNi5 phase. The lattice parameters and cell volumes of the component phases increase with increasing Mn content. P-C-T curves show that the equilibrium pressure for hydrogen desorption decreases from 1.28 atm (x=0.0) to 0.67 atm (x=0.5) with increasing x, and the hydrogen storage capacity increases from 1.19 wt% (x=0.0) to 1.38 wt% (x=0.4). The electrochemical studies show that the maximum discharge capacity increases first from 330.4 mAh/g to 360.0 mAh/g with increasing x from 0.0 to 0.4, and then decreases to 346.9 mAh/g when for x of 0.5. The HRD and the hydrogen diffusion coefficient D of the alloy electrodes increases firstly, then decrease with increasing Mn content, but the charge-transfer reaction resistant Rct decreases firstly, then increases. They imply that the electrochemical kinetics property of the La0.7Mg0.3Ni3.4-xCo0.6Mnx hydrogen storage alloys increases firstly and then decreases with increasing x from 0.0 to 0.5.