A theoretical study of the catalytic activation of hydrogen peroxide on titanium silicalites is presented. Calculations for several peroxide adsorption structures show that the interaction is weak. Formation of cyclic complexes between deprotonated peroxide and solvent molecules or with a silanol group is highly endothermic (more than 90 kJ/mol). The energy barrier of activation for ethene epoxidation with nondissociatively adsorbed peroxide is 83 kJ/mol with hydrogen peroxide over titanium silicalite. This energy is lower than the energy for peroxide deprotonation and implies that O-H bond cleavage during peroxide adsorption on titanium clusters is not necessary.