The purpose of the article is to study the kinetics of the process of desulfurization of steel in steel casting ladles during the release of steel from the steelmaking unit and during its stay in the ladle when refining liquid limestone-alumina slag (CaO + Al2O3) or solid slag forming. It is known that successful desulfurization depends on the chemical composition of the slag, the time of its formation in the ladle, the oxidation of the metal, the conditions of mixing steel in the ladle, additional technological operations, ladle processing. To study the kinetics of the process of desulfurization, industrial studies were carried out in the oxygen-converter shop of PJSC “Azovstal Iron and Steel Works” with the melting of 17Г1СУ steel in 350-ton converters for different metal processing options in steel casting ladles. A total of 1456 smelts were carried out, of which 460 – when treated with synthetic slag (SS), 271 – when treated with solid slag-forming mixture (SSFM), 630 – when used together with SS and SSFM and 94 – without treatment of SS and SSFM. In the treatment of steel in the ladle there were used synthetic slag composition,%: CaO – 47-52; Al2O3 – 32-39, SiO2 – 3-7, MgO – 10-14, MnO + FeO up to 1.5, TiO2 – 4-6, S – up to 0.035 and solid slag-forming mixture (fractions up to 5 mm), consisting of 76–78 % lime containing up to 0.05 % sulfur and 22–24 % fluor-spar – up to 0.1 % sulfur. Mathematical processing of experimental and comparative smelts produced by the method of multiple correlation revealed the influence of each of the factors of the converter process (the basicity of slag B, the specific consumption of lime qlime and fluor-spar qf.s., cast iron temperature), as well as the basicity of converter slag falling into the ladle when draining metal from the converter, its sulfur content (S)s, the specific flow rate of the SS and the SSFM on the sulfur content of the finished metal, which is described by the corresponding equations and is characterized by certain graphic dependencies. Comparative analysis of the desulfurization efficiency of different options in comparison with the variant when the metal was not treated in any way, showed that the amount of sulfur recovered from the metal in the processing of its solid slag-forming mixture, synthetic slag, together slag and mixture increased in 1.36, 2.1 and 2.46 times, respectively. The method of correlation analysis revealed that the specific amount of sulfur recovered when applying solid slag-forming mixture is 14 times higher than when using synthetic slag (with their separate application).