The influence of the Al concentration in the X-Ray Renninger scans (RS) for the GaAlAs/GaAs system is investigated. The RS simulation program MULTX [Defect Control in Semiconductors, K. Sumino (ed.) Elsevier Sci. Pub. (North Holland), 1990, 1535] allows for the better choice of peak/background ratio which shows enough sensitivity to detect Al content changes. The three (000, 002, 111) and four beam (000, 002, 113, 111) peak/background ratios decrease with the increment of the Al content according to the structure factor calculation.