Regioselective photooxidative demethylation of methyl-substituted N-containing heterocyclic compounds is investigated in non-aqueous (ethane nitrile) solutions containing semiconductor oxide (TiO2) as photocatalyst in the presence of molecular oxygen upon irradiation at room temperature conditions. A plausible electron transfer mechanism, in which an electron-hole pair is generated on the surface of TiO2 by illumination, is proposed for the semiconductor-mediated photocatalysis. Molecular orbital calculation by the AM I method has been performed for the electron densities of N-atoms of heterocyclics in the present study.