The effect of FeO on volatilization of PbO from CaO-SiO2-Al2O3-FeO molten slag was studied in a lab-scale electric furnace in N-2 atmosphere at a temperature of 1773 K. The employed slag samples consisted of reagent-grade of CaO, SiO2, Al2O3 and FeO mixed at various weight ratios, whose content was adjusted to 2 x 10(3) mg-PbO/kg-slag. From the experimental results, it was found that the apparent rate of volatilization of PbO determined by time change of PbO content in the molten slag, increased with an increase in slag basicity which was defined by the weight ratio of CaO to SiO2, but decreased when CaO was replaced by FeO. The apparent rate of volatilization of PbO, however, was not significantly influenced by slag viscosity, so far as the weight ratio of FeO to CaO in molten slag was controlled at a value of FeO/CaO higher than 0.38. By a comparison of interaction energies between Pb2+ and Ca2+, Si4+ and Fe2+ in molten slag, it was found that the strength of bondage force between Pb2+ and the other cation was in the order of Si4+ > Fe2+ > Ca2+. Hence, it was considered that the repulsive force between Pb2+ and Fe2+ was lower than that between Pb2+ and Ca2+, which led to a smaller effect of FeO than CaO on volatilization of PbO from CaO-SiO2-Al2O3-FeO molten slag.