This paper presents calculations (CRYSTAL program) on the interaction of formic acid with models for the (110) face of the rutile TiO2 structure. HCO2H strongly dissociates on the surface leading to a formate anion. Thus, the best adsorption mode results from an acidic cleavage contrary to what would be expected from the comparison of the basic and acidic gas-phase cleavages. This occurs since the adsorbed HCO2- is stabilized as a bidentate species; the adsorption involves two oxygen atoms bound to two surface titanium atoms.