The detoxication of pesticides after their application is very important from the environmental, human health and economical points of view. The use of additives that can enhance degradation of the applied pesticides could be useful to clean pesticide residues from fruit surface. As a model we choosed fungicide procymidone and titanium dioxide as additive. Chromatography and spectroscopic techniques were used for identification of phototransformation products and phototransformation pathway with addition of TiO2. Results obtained from experimental research were confirmed by quantum-chemical calculations. Also, quantum-chemical research gave a more detailed information regarding phototransformation pathway of free molecule of procymidone and its molecular complex with surface of TiO2. All the calculations were performed by means of the DFT (B3LYP functional) method using the basis set 6-31G from GAUSSIAN-09 package [1]. Our main results presented in Figures 1 and 2, show that the exited molecule of procymidone is coordinated trough of its Cl* atom to the Ti* atom of the molecular system H2Ti4O9 and interacts with one of the hydroxyl groups that results from water photodecomposition on TiO2 surface. It was found that during this process Cl* is substituted with one OH- group, thus the photoexited molecule of procymidone transforms into its lover toxic phenol derivative.figureFig. 1 The initial geometry of the reacting system: Procymidone x H2Ti4O9 x hydroxide anionfigureFig. 2 The final optimized geometry of the reacting system under investigation