The thermal compatibility of centrifugally atomized U–Mo alloys with aluminum has been studied. Samples of extruded dispersions of 24 vol.% spherical U–2 wt.% Mo and U–10 wt.% Mo powders in an aluminum matrix were annealed for over 2000 h at 400°C. No significant dimensional changes occurred in the U–10 wt.% Mo/aluminum dispersions. The U–2 wt.% Mo/aluminum dispersion, however, increased in volume by 26% after 2000 h at 400°C. This large volume change is mainly due to the formation of voids and cracks resulting from nearly complete interdiffusion of U–Mo and aluminum. Interdiffusion between U–10 wt.% Mo and aluminum was found to be minimal. The different diffusion behavior is primarily due to the fact that U–2 wt.% Mo decomposes from an as-atomized metastable γ-phase (bcc) solid solution into the equilibrium α-U and U2Mo two-phase structure during the experiment, whereas U–10 wt.% Mo retains the metastable γ-phase structure throughout the 2000 h anneal and thereby displays superior thermal compatibility with aluminum compared to U–2 wt.% Mo.