The kinetics of the epoxidation of castor oil in benzene with peracetic acid formed in situ from acetic acid and hydrogen peroxide in the presence of an ion-exchange resin as a catalyst was studied. Eighteen pseudo-two-phase models are established that, besides the main reactions of peracid and epoxy ring formation, also consider the side reaction of epoxy ring cleavage with acetic acid. Kinetic expressions for the heterogeneously catalyzed peracetic acid formation are developed on the basis of Eley-Rideal and Langmuir-Hinshelwood-Hougen-Watson postulates. An equation derived for the temperature dependency of the chemical equilibrium constant for peracetic acid formation is applied. Kinetic and adsorption parameters were estimated by fitting experimental data using the Marquardt method. The best-fit model correctly interprets data of double bond and epoxy group contents as a function of reactant ratios, catalyst concentrations, and temperatures applied during epoxidation. The proposed model better fits experimental data than the pseudohomogeneous model reported in the literature.