The diffusion behavior of &bgr; phase Cu–Al has been studied at 800, 850, and 950 °C using the experimental approach and analysis scheme of Kirkendall and Darken. Diffusion couples were made using the window frame technique and concentration profiles were determined by electron probe microanalysis. The chemical diffusion coefficient,D˜ was found to beD˜=0.65 exp(−42200/RT) cm2/s. The diffusivity was observed to be independent of composition over the range 11–13 wt. % Al. The self‐diffusion coefficientsDCuandDAlwere determined to beDAl=0.13 exp(−38900/RT) cm2/s andDCu=2.2 exp(−43400/RT) cm2/s. All activation energies are in calories/mole.