Equilibrium between CaO-Al₂O₃-TiO_x or BaO-Al₂O₃-TiO_x slags and a liquid Fe-20 mass%Cr alloy with respect to oxygen and nitrogen was studied at 1873 K as a function of Ti (or Al) content in alloys, using an Al₂O₃ crucible. The Al-O and Ti-Al relations in liquid alloy were studied, and nitride capacity defined by C_N=(mass%N)·P_O2^3/4/P_N2^1/2 was obtained from nitrogen distribution ratios, coupled with the analyzed oxygen content in liquid alloy or the P_O2 determined by Ti/TiO₂ equilibrium. Based on these results, activity of Al₂O₃ and activity coefficients of TiO₂, TiO_1.5 and CrO_1.5 were evaluated.