In this work a numerical simulation program was developed to model the simultaneous diffusion and reaction behavior of methanol in 88% hydrolized polyvinyl alcohol using the finite difference approach. The simulation results were obtained for a temperature of 110oC, a methanol activity of 0.12, and a total sample thickness of 0.01821 cm. The results were compared with experimental data, and a sum of least square regression gave a reaction rate constant of 1.58·10–3 cm3 mol–1 sec–1 for the second order reaction between methanol and vinyl acetate. The agreement between experiment and simulation was greatly improved by accounting for possible methanol desorption due to crystallinity changese in the polymer during the experiment. The simulation was also investigated as a tool for reducing the experimentation time.