The application of Laser-Induced Breakdown Spectroscopy (LIBS) for multi-elemental analysis of Electric Arc Furnace (EAF) slag was investigated. Industrial EAF slag samples were analyzed by Inductively Coupled Plasma - Optical Emission Spectrometer (ICP-OES) for the major elements: Al, Mg, Mn, Fe, Si & Ca (Si was determined by FAAS - Flame Atomic Absorption Spectrometer) and were used as the main calibration samples of a laboratory LIBS system. The effect of different parameters on the obtained calibration quality was experimentally tested; namely sample preparation methodology, sample matrix effect coming from the use of different fluxes in the EAF production process as well as from the complementary use of certified reference materials (CRM) standards, and data elaboration of the LIBS signal. Pressed pellets of fine-grained slags (granulometry <125μm) combined with KBr binder were found to reduce the matrix effect associated with the inhomogeneity in EAF slag samples. The different matrix in the industrial slag samples formed by different applied steelmaking fluxes (lime, dolomitic lime) proved to affect the LIBS analysis for some elements especially Fe, Mn and Ca. Data normalization with combinations of the primary elements spectral peak improved the linearity of the calibration curves.