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The coarsening process of the NiAl ordered b9 precipitates was studied in the isothermally aged Fe-10 wt-%Ni-15 wt-%Al and Fe-10 wt-%Ni-15 wt-%Al-1 wt-%Cu alloys. The aging treatments at 750, 850 and 950uC caused the precipitation of the b9phase in a ferritic matrix. In general, the coarsening process of Cu containing alloy was slower with an activation energy of 248 kJ mol 21 compared to 194 kJ mol 21 for the other alloy. However, the coarsening kinetics for the former alloy was faster at 950uC. The precipitation hardening response was also better in the Cu containing alloy, with a slower overaging stage. The coarsening kinetics followed the behaviour predicted by the modified Lifshitz-Slyozov-Wagner theories for coarsening controlled by volume diffusion.