The sulfide morphology in Cu-Sn-Zn-S alloy castings was investigated to understand the transition from eutectic solidification to monotectic solidification. The sulfide morphology was observed to clarify whether sulfides were formed by eutectic reaction or monotectic reaction. The cooling rate during solidification was changed by changing mold materials, mold shapes, and mold sizes. The holding time from deoxidation of melt to casting was changed to understand the effect of deoxidation on the sulfide morphology. Eutectic sulfides were formed when the melt was cooled slowly, and the amount of monotectic sulfide increased with increasing cooling rate. The transition from eutectic morphology to monotectic morphology occurred at cooling rates of 0.5K/s to 1.0K/s. Just after deoxidation with Cu-P alloys, sulfides were formed by monotectic reaction. However, with increasing holding time of the melt after deoxidation, the amount of the sulfides formed by eutectic reaction increased.