We report the results of a detailed x-ray diffraction analysis of two AlxIn1-xAsySb1-y/GaSb multilayer samples grown by molecular beam epitaxy on GaSb (100). The kinematical scattering theory was used to fit the x-ray diffraction intensity profiles to determine the lattice spacing, composition, and strain of the multilayers, allowing for interdiffusion between the layers and variation in the multilayer wavelength. It has been determined that the quaternary alloy composition varies throughout the layer and that there is an interfacial quaternary layer that differs in composition from that of the bulk AlxIn1-xAsySb1-y layer. A rationale for this graded composition and interfacial layer will be discussed based on the growth dynamics for this system. (c) 2006 American Vacuum Society.