tThe identification and intensity estimation of some aluminium emission lines have been proposed toperform an on-line quantification of the Al contribution to the laser-welding process of Usibor blanks.This boron steel is protected by an Al-Si coating that is removed by laser ablation before welding. If thisprocess fails to remove Al from the joint surface, its contribution may affect the final properties of theresulting seams, therefore compromising their quality. Experimental tests have been performed, some ofthem in a real production scenario. They have been analysed and compared to the results of welding testspecimens, analysis of the associated tensile properties and fracture locations and seam macrographs.These studies have indicated that on-line quantification of the Al contribution to the process is feasibleand that a correlation can be established between the Al content estimated in real-time and the resultsderived from the off-line tests considered