The study aimed to evaluate the antioxidant activity (in vitro) of vegetable oils containing conjugated linolenic acid (CLnA) isomers such as α-eleostearic and punicic acid and also to evaluate the comparative effectiveness of these vegetable oils due to presence of cis-trans isomers in variable amount. Different in vitro methods were used to evaluate the free radical scavenging activity, hydroxyl radical scavenging activity, metal chelating activity and reducing activity of oils at different concentrations of CLnA isomers such as 125, 250 and 375μg/mL. Inhibition on lipid peroxidation was evaluated by measuring thiobarbituric acid responsive substance (TBARS) and conjugated diene formation at 125 and 250μg/mL concentrations of CLnA. Both the oils showed potent free radical scavenging activity at 375μg/mL concentration. In contrary, these oils showed higher hydroxyl radical scavenging, metal chelation and reducing activity at lower concentration i.e. 125μg/mL. TBARS formation and conjugated diene formation was lower i.e. inhibition of lipid peroxidation was maximum at 125μg/mL of both CLnA isomers. Overall, both the oils showed better antioxidant activity at lower concentration due to better oxidative stability and bitter gourd oil showed more prominent antioxidant activity than snake gourd oil due to presence of higher trans content. © 2011 Elsevier Ltd.