Abstract The interdiffusion in a low-strained Si0.93Ge0.07/Si epilayer was analyzed by double-crystal X-ray diffraction. The interdiffusion was characterized by a low diffusion barrier of 1.81eV with a diffusion constant of 4.3105cm2/sec, which indicates correlation with the stacking fault generated by the homoepitaxial growth of the Si layer prior to the growth of the strained SiGe layer. At the very low-strained layer, the driving force causing the interdiffusion is the concentration gradient, and the mechanism is self-diffusion of Si. Furthermore, the interdiffusion mechanisms were classified into three groups, depending on the Ge mole fraction x. For x0.2, the diffusion process in the SiGe alloy is similar to a self-diffusion of Si atoms, while, for 0.2x0.4, Ge atoms prefer to be diffused out from the alloy. Finally, for x0.4, Si atoms can be diffused into the alloy.