The X-ray powder diffraction data of the compound GdAlSi was studied by means of X-ray diffraction technique and refined by Rietveld method. The compound GdAlSi has tetragonal alpha-ThSi2-type structure, space group I4(1)/amd (No. 141), Z = 4, the lattice parameters a = 0.41234 (1) nm, c = 1.44202(1) nm. The Smith and Snyder figure of merit([5]) F-N is F-30 = 252.1(36). The R-factors of Rietveld refinement are R-p = 0.098 and R-wp = 0.128. The X-ray powder diffraction data are given. The field dependence of the magnetization measured at room temperature and the temperature variation of the inverse magnetic susceptibility of the compound GdAlSi were also presented.