Interference effects of coexisting elements on emission spectrochemical analysis for steel were studied. Binary (Fe-X) and ternary (Fe-X-Y) samples made with Ar-Arc furnace were used for experiments. The effects of C, Mn, Ni, Cr, and Mo on S, of Si, Mn, Cr, and Mo on Nb, of Mn, Cu, Ni, Cr, and Mo on P, and of Mn, Ni, Cr, and Mo on V were investigated. In many cases interference effects were due to the neighbouring line of coexisting element. Multiplicative interference was observed between S and C, and between Nb and Mo, and the difference between obtained values and the values certified by chemical analysis were expressed as follows: ΔS=f (C, S), ΔNb=f (Nb, Mo). The approximation correction method to correct the difference caused by the multiplicative interference was proposed and applied to routine analysis. It is indicative from this study that the unification of calibration curves can be made, regardless of materials which were subjected to different metallurgical treatments.