Molecular orbital calculations to predict the activation energy of silylation are performed. The activation energy for polyvinylphenol is predicted to be 19.6 kcal/mol at the MP-2 (the second-order Moller-Plesset perturbation theory) level, and this value is in good agreement with an experimental value of 19.4 kcal/mol. Theoretical values calculated from the Hartree-Fock and nonlocal density functional theories are found to be larger than the experimental value by about 15 kcal/mol and 5 kcal/mol, respectively. Thus, the MP-2 level of calculation is required for a quantitative prediction of the activation energy of silylation. Comparison between the theoretical and experimental values further showed that the rate-determining step of the silylation is the diffusion when pure polyvinylphenol is silylated, whereas it is the reaction when additives are mixed to polyvinylphenol. This result shows that the theoretical calculations become a tool for clarifying the kinetics of silylation, and can be used for designing new materials. The activation energy of silylation for carboxylic acid and alcohol is also predicted, and experiments to silylate polyvinylalcohol are performed. It is shown that the alcohol unit can be silylated with a higher activation energy than that for polyvinylphenol, whereas for carboxylic acid, significant desilylation may occur after the silylation.