The rate of desulfurization was investigated by allowing liquid iron droplets to fall through a CaO-Al₂O₃-MgO slag layer at 1600°C. Droplet falling velocity decreased by increasing the sulfur content in the metal. The sulfur transfer was well represented by a first order reaction rate with respect to the sulfur concentration of the metal. The rate of desulfurization during dynamic contact while falling through the slag layer was about two orders of magnitude larger than that of the static contact between the metal and slag. The enhanced rate of desulfurization during the dynamic contact was attributed to the combined effect of (1) the continual contact of fresh slag while falling, (2) enhanced internal circulation in the metal phase, and (3) most importantly, emulsification of the metal/slag interface, which greatly increases the reaction area. The rate of desulfurization was affected to a large extent by slag composition. It was tentatively concluded that slag composition influences the rate of desulfurization by affecting both emulsification of the metal/slag interface and the interfacial reaction of sulfur transfer.