La1-xSmxMgNi3.6Co0.4 (x = 0-0.4) alloys were prepared by vacuum intermediate frequency induction furnace with a high purity helium gas as the protective atmosphere. The effects of partially substituting Sm for La on the phase structure, morphology and hydrogen storage properties of the alloys were investigated systematically. The detections of XRD and SEM reveal that the as-cast alloys contain two phases LaMgNi4 and LaNi5. The hydrogen storage capacity of the alloys decreases with increasing Sm content, namely 1.859, 1.707, 1.585, 1.578, 1.471 wt. %, respectively corresponding the variation of Sm content. The P-C-T curves of the alloys show flat plateaus corresponding to the absorption/desorption pressure plateaus of the LaMgNi4 hydride. Meanwhile, the enthalpy change (ΔH) and entropy change (ΔS) of the LaMgNi4 hydrides for hydriding decrease from -40.37 kJ/mol (x = 0) to -26.99 kJ/mol (x = 0.4) and from -101.9 J/mol/K (x = 0) to -77.56 J/mol/K (x = 0.4), respectively. The electrochemical measurement displays that the maximum discharge capacity of the alloy electrodes declines from 347 mAh/g to 270.5 mAh/g, to be very similar with the trend of the gaseous hydrogen absorption capacity. On the contrary, the cycle stability of the as-cast alloys obviously augments with the Sm content increasing, which can be attributed to the facilitated corrosion resistance by Sm substituting.