Intramolecular H-transfer reactions in cis-HO3 and CH2OO were studied at the MP2 and B3LYP levels of theory. Activation energies (E a) and Gibbs free energies of activation (∆G #) of the H-transfer reactions were calculated. The activation energies of the H-transfer in cis-HO3 and CH2OO were about 110 and 130 kJ/mol, respectively. Catalytic effects of some protic molecules including HCOOH, CH3OH, NH3, CH3NH2, HOCl, H2O2, and H2O, on the activation energies and transition state structures were studied. The more stable transition state structures were obtained in the presence of the protic molecules. Our calculations showed that the protic molecules decrease the activation energies of the H-transfer reactions about 50 kJ/mol.