Metal oxide complexes have high catalytic potential in many fields, such as oxidation, dehydrogenation, dehydration, reductive coupling, etc. The adsorption of molecules is a fundamental process in catalytic reactions on the metal oxide complex. In this study, water adsorption and dissociation processes on small Mn-doped TiO2 complexes are investigated at the density functional theory (DFT) level of theory. Water adsorption at terminal Mn atoms is typically found to have an energy around -0.7 eV, which is smaller than the -1.2 eV observed at terminal Ti atoms. Dissociation energies at Mn atoms are determined to be about -0.6 eV, which are also smaller than the approximately -1.2 eV dissociation energies at Ti atoms. Molecular adsorption without dissociation is favorable in energy after water adsorbs at each metal atom. Mn doping reduces the reaction energy; the reaction energy of the doped system is not similar to that of the pure manganese oxide complex.