In order to clarify the experimental observation that molecules of vinclozolin decay by their adsorption on polycrystalline TiO2 surface we have investigated quantum-chemically the electronic structure of free molecule of vinclozolin (I) and its molecular complex with TiO2: 3,5C6H3Cl2-N(CO)2OC(CH3)(C2H3) ― Ti4O8 (II). All the calculations were performed by means of the DFT (B3LYP functional) method using the basis set 6-31G from GAUSSIAN-09 package [1]. It has been shown that the coordination of the system (I) to one of the end titanium atoms of the inorganic linear system Ti4O8 is being realized by means of the oxygen atom O1 (see Fig. 1) . The above coordination leads to the splitting of the C-O bond between the oxygen atom O2 and the non-carbonyl carbon atom C3 of the five-membered heterocycle of (I). The formation of the system (II) is being also accompanied by the transfer of the negative charge (0.20 e) from the organic part of (II) to the Ti4O8 one. Our conclusion about the splitting of the given C3-O2 bond has the indirect confirmation based on the results obtained from the LC-MS chromatography. Thus, the above calculations allow one to understand the initial stage of decomposition of molecules of vinclozolin by their adsorption on TiO2 surface.