Abstract The oxidation of meta-phenylphenol (m-PP) and para-phenylphenol (p-PP) was photosensitized by excitation at 365 nm in the presence of azidopentaammine cobalt(III) in neutral aqueous solution. The presence of m-PP or p-PP did not affect the initial quantum yield of cobalt(III) reduction, and oxygen had no apparent effect. By electron spin resonance spectroscopy upon irradiation, it was possible to detect the formation of both N3+ and m-PP+ radicals as adducts with the spin trap 5,5-dimethyl-1-pyrroline-N-oxide. Laser flash photolysis experiments gave evidence of the formation of the corresponding phenylphenoxyl radical by reaction between N3+ and the phenols, and their constants of formation and decay were calculated. The dimers were identified as the major photoproducts. Trimers and tetramers of m-PP and p-PP were also formed. It is worth noting that no formation of quinones was observed. Cobalt appeared to prevent the reaction of oxygen with the phenoxyl radicals.