Despite the role of reactive oxygen species in the development of respiratory distress syndrome (RDS) and bronchopulmonary dysplasia (BPD) in preterm infants, the anti-oxidant properties of commercial surfactants have never been studied. We measured the superoxide dismutase (SOD) and catalase (CAT) activity, the scavenger activity against hydrogen peroxide (H2O2), and its changes after the addition of SOD and CAT in four natural surfactants, namely Infasurf, Curosurf, Survanta, and Alveofact. We found that they contain measurable amount of SOD and CAT. Curosurf and Survanta seem to have higher antioxidant effect than Infasurf and Alveofact. Moreover, the highest phospholipid concentration and recommended dose of Curosurf imply that its scavenger activity for each treatment dose in preterm infants is likely higher than that of Survanta. Finally, the supplementation with SOD and CAT induced a remarkable increase of antioxidant action in all studied surfactants. Pediatr Pulmonol. 2009; 44:1125–1131. ©2009 Wiley-Liss, Inc.