A mathematical model of the process of low-temperature carbonization of sulfur-bearing oil shales in a fluidized-bed retort, which takes account of the characteristics of hydrodynamics and heat exchange in the thermal shale decomposition process as well as the kinetics of thermal degradation of the organic matter, is developed. A block diagram of the calculation algorithm and the results of numerical experiment based on the developed mathematical model are presented. It is shown that the properties of the sulfur-bearing shale and the conditions of the low-temperature carbonization process affect the parameters of the fluidized-bed retort.