This study investigates the adsorption and reactions of H2O 2 on TiO2 anatase (101) and rutile (110) surfaces by first-principles calculations based on the density functional theory in conjunction with the projected augmented wave approach, using PW91, PBE, and revPBE functionals. Adsorption mechanisms of H2O2 and its fragments on both surfaces are analyzed. It is found that H2O 2, H2O, and HO preferentially adsorb at the Ti 5c site, meanwhile HOO, O, and H preferentially adsorb at the (O 2c)(Ti5c), (Ti5c)2, and O 2c sites, respectively. Potential energy profiles of the adsorption processes on both surfaces have been constructed using the nudged elastic band method. The two restructured surfaces, the 1/3 ML oxygen covered TiO2 and the hydroxylated TiO2, are produced with the H2O 2 dehydration and deoxidation, respectively. The formation of main products, H2O(g) and the 1/3 ML oxygen covered TiO2 surface, is exothermic by 2.8 and 5.0 kcal/mol, requiring energy barriers of 0.8 and 1.1 kcal/mol on the rutile (110) and anatase (101) surface, respectively. The rate constants for the H2O2 dehydration processes have been predicted to be 6.65 × 10-27 T4.38 exp(-0.14 kcal mol-1/RT) and 3.18 × 10-23 T5.60 exp(-2.92 kcal mol-1/RT) respectively, in units of cm3 molecule-1 s-1.