The kinetic model for the synthesis of bis(2-ethylhexyl) phthalate from phthalic anhydride and 2-ethylhexanol in the presence of methane sulfonic acid as a catalyst has been derived, based on the investigation carried out in an isothermal, semibatch reactor. The first step, the formation of mono(2-ethylhexyl) phthalate, is very fast and irreversible. The second step, the esterification of monoester with 2-ethylhexanol, is relatively slow and needs a catalyst. The second reaction appears to be of the first order with respect to mono(2-ethylhexyl) phthalate and does not depend on the concentration of alcohol.