The adsorption and reaction of H2S on TiO2 rutile (110) and anatase (101) surfaces have been investigated by using periodic density functional theory (DFT) in conjunction with the projected augmented wave (PAW) approach. Adsorption mechanisms of H2S, HS, and S on both surfaces were analyzed. It was found that H2S, HS, S, and H preferentially adsorb at the Ti5c, O2c, (Ti 5c)2, and O2c sites, respectively, on the rutile surface, and at the Ti5c, (Ti5c)2, (-O2c)(-Ti 5c), and O2c sites, respectively, on the anatase surface. Potential energy profiles of the adsorption processes on both surfaces producing H2 and H2O were constructed using the nudged elastic band (NEB) method. Forming surface sulfur species by a complete O ↔ S exchange at the rutile surface is endothermic by 15.4 kcal/mol and requires a high energy barrier of 35.5 kcal/mol, while it is endothermic by 5.0 kcal/mol and requires a lower energy barrier of 12.4 kcal/mol at the anatase surface. The rate constants for the dehydrogenation and dehydration processes have been predicted.