The elements of Cu and Sn are two of the main residual impurities in steel, especially in recycled scrap steel. Sulfur is one of the main impurities in steel, and it may result in a large emission of slag and CO₂ to remove sulfur from steel. Utilization of these elements has been an important and difficult matter for metallurgist. In the present paper, the as-cast steels containing different concentrations of Cu, S and Sn are prepared in laboratory. The effect of Sn addition on sulfide precipitation is investigated and discussed with respect to the morphology, size, and composition of sulfide. The experimental results show that the addition of Sn suppresses the sulfide precipitation at high temperature, promotes more copper bearing and smaller sulfides precipitation at low temperature. On the other hand, sulfide precipitates are shown to reduce the micro-segregation degree of Sn in steel, which may be because Sn dissolves in sulfide to some extent and sulfide particles provide more interfaces for Sn to distribute.