This Technical Report describes a X-ray fluorescence (XRF) spectrometric method for the determination of Si and Al contents in Ferro Silicon materials. The method is applicable to: - Si content between 40 and 90 %; - Al content between 0,5 and 6 %.The Technical Report specifies the general requirements for analysis by X-ray fluorescence spectrometry and the preparation of the test sample.The correction of the spectrometric measurement from spectral interferences on the analytical lines used is essential. This Technical Report is valid for the analytical lines: - Si Kα 7.126 (for element contents between 45 and 90 %);- Al Kα 8.339 (for element contents between 0,8 and 6 %);- Fe Kα 1.937 (for element contents between 10 and 58 %).NOTEFor matrix matching purposes, iron is included in the analytical program to be prepared.Within the conditions here above, spectral interferences don’t need to be calculated.