The discovery that certain cellobiose 2-epimerases (C2E) are capable of synthesizing lactulose and epilactose with high yield and selectivity has renewed the interest in their biological synthesis. In order to provide a valuable tool for the design and optimization of the synthesis of lactulose and epilactose with C2E as biocatalyst, the reaction is modeled here for the first time. Two competing reaction mechanisms, so called extended and reduced mechanisms, were proposed and their corresponding models developed. The extended mechanism was discarded because of the overfitting of the resulting model. The parameters of the reduced model were successfully estimated by no linear regression at 30, 40, 50, 60 and 70 degrees C, and the temperature dependence of the kinetic parameters was modeled by fitting them to Arrhenius and Vant ' Hoff-type equations. The reduced model showed a good fit to experimental data within the studied temperature range, well describing the course of reactions.