The formation of U(Al, Si)2 and U(Al, Si)3 and their growth kinetics have been investigated by means of hot dipped diffusion couples of U3Si and aluminium in the temperature range 510 to 670-degrees-C. The penetration width of aluminium and the chemical composition of the growing phases were determined with SEM in connection with EDAX and WDX techniques. Aluminium atoms diffused faster into grain boundaries of U3Si than uranium or silicon did into aluminium and proved to be dominant moving species in the growing U(Al, Si)3 phase. U(Al, Si)2 was first formed at grain boundaries of U3Si by the diffusion of aluminium and grew finally to form U(Al, Si)3 by further diffusion of aluminium. The order to disorder transformation of the U(Al, Si)3 phase helped the recrystallization process to occur. Optical microscopy permitted to distinguish the single phase region of recrystallized grained U(Al, Si)3 from the neighbouring multi-phase region composed of U3Si, U(Al, Si)2 and U(Al, Si)3. The growth of the multi-phase region as well as of the U(Al, Si)3 phase obeyed a parabolic rate law. The activation energy governing the growth of the U(Al, Si)3 phase was calculated to be about 220 kJ/mol.