The evolution of the molecular structure of molybdena/titania catalysts prepared by the equilibrium-deposition-filtration (EDF) method is monitored by in situ Raman spectroscopy in the temperature range 25-430°C. The study is based on a recently proposed picture for the interfacial speciation of Mo(VI) oxo-species deposited at the "titania/electrolytic solution" interface of "wet" catalyst pastes and on the temperature-dependent features of in situ Raman "snap-shots" obtained with increasing temperature. The configurations of the deposited Mo(VI) oxo-species on "wet" (i.e. prior to drying) samples conform to the theoretically previewed speciation for the respective pH's and concentrations of the precursor electrolyte and impregnating solutions; for initial Mo(VI) concentrations up to 2.5×10-2 M the predominant deposited species evolve from monomeric MoO42- ions retained above a bridging surface hydroxyl through a hydrogen bond [Ti2OH...O-MoO3] (for solution pH=9) to a mixture with inner sphere mononuclear mono-substituted (with the terminal surface oxygen of titania) complex [Ti-OMoO3] (for solution pH=6) and to a simultaneous occurrence of the former monomeric species with Mo7O246- and HMo7O 245- (for solution pH=4). A gradual transformation of the complex configurations is monitored with rising temperature by in situ Raman snap-shots and the spectra of the final calcined samples exhibit the features of dispersed mono-oxo (Ti-O)3Mo=O species. A low presence of associated species (possessing Mo-O-Mo linkages) is evident for the higher loaded samples.