Metal oxide photocatalysts TiO2/MoO3 and TiO2/MoO3:V2O5 have been investigated by electron paramagnetic resonance (EPR) spectroscopy under in situ light excitation. Structural identification of all paramagnetic centers (PCs) recorded, such as surface and lattice Ti3+ ions as well as Mo5+ and V4+ ions and nitrogen N-14 atoms containing the unpaired electron (N-center dot-radicals), have been performed. The temperature behavior of PCs in the range of 30-300K and photoinduced changes of EPR spectra under light irradiation have been investigated. The validity of the Curie law was confirmed for the PCs of such composite photocatalysts. A new original method of detection of charge carrier separation and accumulation is suggested using EPR-technique. It is shown that TiO2/MoO3 and TiO2/MoO3:V2O5 photocatalysts are capable to accumulate photogenerated charge providing fresh possibilities for practical applications in photocatalysis because these oxide heterostructures retaining oxidation activity for a long time (more than 5h) under the dark conditions after illumination. [GRAPHICS] .