The reaction kinetics between nitrogen gas and Nd(Fe, Mo)12 intermetallic compound has been studied. The relationship between the reaction temperature, the reaction time with average mass fraction of N in samples have been measured. The activation energy of first step reaction, Ef,(18.2 kJ/mol), is smaller than Es (64.6 kJ/mol) of the second step during which nitrogen diffusion in the range 400~550℃ can be represented by an activated interstitial diffusion process. Heating above 550℃ leads to disproportion of the compound into NdN and α-Fe and the permanent properties will be damaged greatly.