In order to predict the antioxidant activity of 7 polycyclic lactams, a two dimensional quantitative-structure activity relationships (2D-QSAR) study based on a 5-descriptor model was performed. The synthetic compounds built from a condensed lactam scaffold were screened for their abilities to inhibit the autoxidation of pyrogallol, a superoxide anion radical-dependent process. The ketone 2 (8,9-dihydro-7H-benzo[de]pyrrolo[1,2-a]quinoline-7,10(7aH)-dione) exhibited the most potent antioxidant activity in vitro. The oxidation mechanism was proved by the isolation and characterization of alcohol 5 formed in the reaction of ketone 2 with dissolved oxygen in methanol.