The grain growth of an electrodeposited nanocrystalline Fe–Ni invar alloy was studied with differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The results showed very limited grain growth below the temperature of 0.36T m , and the activation energy was 40±3kJ/mol in the low temperature range, which implied the possible mechanism of grain growth as re-ordering of grain boundaries; an abrupt grain growth happened above 0.36T m with a DSC exothermic peak detected, of which the heat release was about 14±2J/g; at temperatures above 0.36T m , the grain growth activation energy was obtained through Kissinger analysis and isothermal kinetics analysis, both of the results suggested the grain growth mechanism as grain boundary diffusion.