The mathematical model of thermal sterilization of aqueous suspensions of Bacillus stearothermophilus spores was identified. Experimental results of the sterilization process carried out in glass capillaries at temperature ranging from 115 to 125 degrees C were used. To describe the process, a model of subsequent reactions with spores being an intermediate product (Shull model) was applied. It is assumed that activation and destruction are the first-order reactions and the dependence of rate constants on temperature is described by the Arrhenius equation. The model well describes experimental results and the obtained values of the activation energy are in agreement with respective data quoted in the literature.