The reaction of a series of hydroxy-substituted polycyclic aromatic hydrocarbons(PAHs)with nitric oxide containing trace O 2 was carried out in CH 2Cl 2 at room temperature. The products identified by IR, NMR and HRMS indicate that the mono nitration at para- or ortho-position with respect to hydroxy group on the benzene ring occurred regioselectively. The reactions are assumed to be initiated by single electron transfer and the reaction intermediates may be resonance stabilized phenoxy-like radicals.