In this study, La0.75Ce0.25Ni5−xMnx (x = 0, 0.1, 0.2, 0.3) alloys were prepared by vacuum arc melting. The effect of the addition of Mn on the alloy microstructure and hydrogen absorption/desorption properties were explored by characterizing X-ray diffraction (XRD), scanning electron microscopy (SEM), laser particle size test, hydrogen absorption kinetic test, and P-C-T test. The XRD results show that the series of alloys are single-phase alloys composed of the LaNi5 phase, and the cell volume of the alloy gradually increases as the amount of Mn replacing Ni increases. The P-C-T curve of the alloy shows that the alloy has obvious hydrogen absorption/desorption plateau regions, which gradually decrease with increasing Mn content, while the hydrogen storage capacity remains unchanged. The hydrogen absorption kinetic curve of the alloy was tested, and it was found that the hydrogen absorption rate of the alloy increased with the increase of Mn content. These studies show that doping the Mn element in the La0.75Ce0.25Ni5−xMnx (x = 0, 0.1, 0.2, 0.3) alloys may regulate plateau pressure without affecting the hydrogen storage capacity or kinetics properties, providing a reference for the application of this type of alloy in hydrogen pressurization, purification, etc.