As a fundamental study to elucidate the behavior of several minor elements in the oxygen-smelting process of nickel sulfide ore, equilibrium distributions of Cu, Ag, Co, As, Sb and Bi between the iron-silicate base slag with saturated silica and Ni₃S₂–FeS matte phases in a magnesia crucible were investigated at 1573 K under controlled partial pressures of S₂, O₂ and SO₂ with 10.1, 50.7 and 101.3 kPa. The distribution ratio of X, L_X^s⁄m, defined as (mass%X in slag)/{mass%X in matte}, were plotted in relation to the nickel content in the matte (matte grade) and compared with the available data. At a fixed p_SO2, the distribution ratios of Cu, Co, As and Sb increase slightly with increasing matte grade, and in the cases of Ag and Bi, L_X^s⁄m decrease with increasing matte grade up to about 45 mass%Ni and then increase in the higher range. When the matte grade is specified, the distribution ratios of Co, As, Sb and Bi increase with increasing p_SO2 while L_Cu^s⁄m and L_Ag^s⁄m are almost independent of p_SO2. The Raoultian activity coefficients of either metallic or sulfide species of the minor elements in the matte phase were derived, based on a thermodynamic analysis of the experimental distribution data. The sulfide species of cobalt in the matte was estimated to be CoS_2⁄3.