The consequences of photoirradiation of resins and asphaltenes from the heavy catalytically cracked gas oil fraction of a vacuum distillate and heavy pyrolysis tar of straight-run gasoline from Baku crude oil were studied by IR spectroscopy. It was found that exposure to light results in intramolecular rearrangement, leading to the formation of stable polycondensed aromatic functional quinonoid and phenolic structures which exhibit an antiradical activity. The effect of enhancement of the inhibiting activity of resins and asphaltenes as a result of photoirradiation is illustrated by the model test reaction of polystyrene oxidation.