Supersaturated solid solutions of Cu-44.5at.%Ni-22.5at.%Fe and Cu-37at.%Ni-6at.%Cr alloy were produced by ball milling of a pure chemical elemental mixture for 1080 ks. Two fcc supersaturated solid solutions with a grain size of about 20 and 50 nm, respectively, were obtained after milling. These alloys were subsequently aged at temperatures between 800 and 1003 K for different times. The aging promoted the phase decomposition of the supersaturated solid solution into a mixture of Cu-rich and Ni- phases in both the aged MA alloy powders. The growth kinetics of the modulation wavelength was determined from the X-ray diffraction results and followed the Lifshitz-Slyozov- Wagner theory for a diffusion-controlled coarsening in the mechanically-alloyed Cu-Ni-Fe alloy after aging. However, the sidebands intensity seems to be very low and overlapped with the peaks corresponding to the Cu-rich phase in the aged mechanically-alloyed Cu-Ni-Cr alloy. The growth kinetics of composition modulation wavelength for the aged MA Cu-Ni-Fe alloy was faster at 803 and 898 K than that for the same alloy composition obtained by a conventional processing and then aged at the same temperatures.