Stem bark of Cinchona sp. (Rubiaceae) is one of the well known drugs for its therapeutic values intraditional as well as modern medicine. Even though a lot of work has been carried out onquinoline alkaloids of Cinchona, its phenolic constituents received very little attention. In thepresent study, we evaluated antioxidant properties of C. officinalis stem bark methanolic extractand water extract containing phenolic compounds (total phenolics 21.37, 5.18% w/w respectivelyin the two extracts) in different in vitro and ex vivo models viz., antiradical activity by DPPHreduction, superoxide radical scavenging activity in riboflavin/light/NBT system, nitric oxideradical scavenging activity in sodium nitroprusside/Greiss reagent system and inhibition of lipidperoxidation induced by iron-ADP-ascorbate in liver homogenate and haemolysis of erythrocytesinduced by phenylhydrazine in erythrocyte membrane stabilization study. Both the extractsexhibited very good antioxidant activity in all the models tested. The phenolic compoundsincluding tannins present in the stem bark seem to offer protection from the oxidative damage.