Abstract: Mg-based hydrogen storage alloy powder was microencapsulated successfully with a Ni-P composite layer in acid solution containing F^- ion. The weight increase of Ni-P microencapsulated layer could be controlled easily. The content of P in the microencapsulated layer was 3～5%. The x-ray diffractionanalysis (XRD) indicated that the crystal structure of Mg-based alloy was not affected in process of microencapsulating. The SEM images showed that surface of coated alloy powder was encapsulated compactly by spherical particles, while the surface of uncoated alloy powder particle was smooth. The XPS analysis indicated that the Ni in coated layer is of free state. The encapsulated Mg-based alloy powder was of great anti-corrosion ability in the base solution.