A Ni B coating was prepared using chemical plating. XRD analysis shows that the microstructure of as coating is a mixture of amorphous and supersaturated solid solution. The microstructural transformation and properties of the coating for different heat treatment conditions are discussed in details. Ni 2B formed during high temperature ageing. Room temperature ageing was also observed. The age hardenability depends on existence and quantity of Ni 2B, and the transformation mode from Ni 2B to Ni 3B.