Abstract: Laser-induced breakdown spectroscopy (LIBS) is a useful technique for accurate sorting of metal scrap by chemical composition analysis. In this work, a method for intensity-ratio- based LIBS classification of stainless steel applicable to highly fluctuating LIBS signal conditions is proposed. The spectral line pairs for intensity ratio calculation are selected according to elemental concentration and upper levels of emission lines. It is demonstrated that the classification accuracy can be significantly improved from that of full-spectra principal component analysis or intensity-based analysis. The proposed method is considered to be suited to an industrial scrap sorting system that requires minimal maintenance and low system price.