Magnetic Ni@NixPy), core-shell microstructures were successfully synthesized by a simple low-temperature phosphidation route, employing Ni nanospheres as the initial nickel source, NaH2PO2 center dot H2O as the phosphorus ion source. The phosphidation reaction was carried out in N-2 atmosphere at 300 degrees C for 2 h. Experiments showed that the initial Ni/NaH2PO2 molar ratio could strongly affect the phase of the final product. When the Ni/NaH2PO2 molar ratio of 1:2.77 was used, hexagonal Ni2P phase was obtained; while the Ni/NaH2PO2 molar ratio was 1:5.54, hexagonal Ni5P4 phase was produced. It was found that the magnetic properties of the products gradually decreased with the conversion from Ni nanospheres, to Ni@Ni2P and to Ni@Ni5P4. Moreover, initial Ni nano spheres, Ni@Ni2P and Ni@Ni5P4 core-shell microstructures presented outstanding catalytic activities for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in excess NaBH4 solution. Ni@Ni5P4 core-shell microstructures owned the best catalytic activity.