The purpose of the present study is to examine the oxidative behavior of punicic acid (9 cis, 11 trans, 13 cis-18:3 octadecatrienoic fatty acid) under in vivo condition using male albino rats after blending with dietary soybean oil. Male weanling Charles Foster rats (n = four to eight), weighing 65-68 grams, were allocated for fourteen weeks to diets containing 0.6, 1.2 and 2.4% (by weight) punicic acid obtained from snake gourd seed oil (Trichosanthes anguina) after mixing with soybean oil, vis-à-vis control group consisting of 100% soybean oil, containing 50.3% C18:2, 6.2% 9 cis, 12 cis, 15 cis-18:3 (linolenic acid) and does not contain punicic acid. Increase in weight remained higher than control in rats fed with 0.6 and 1.2% punicic acid throughout the experimental period. There was significant lowering in plasma total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) in the groups fed with 2.4% punicic acid. Lipoprotein oxidation susceptibility or LOS expressed as nmoles of malondialdehyde (MDA) per mg of non-high density lipoprotein cholesterol (non-HDL-C) and plasma lipid peroxidation or PLP expressed as nmoles of MDA per ml of plasma exhibited maximum antioxidant efficiency at 1.2% punicic acid, being equivalent to that of control (100% soybean oil). While LOS expressed as nmoles of MDA decreased significantly (except at 2.4% punicic acid level) with the least oxidation at 0.6% punicic acid, with respect to control. Accordingly, punicic acid seemed to be acting both as pro-oxidant (at 1.2% punicic acid level) and antioxidant (at 0.6% punicic acid level), with significant decrease in TC and LDL-C at 2.4% punicic acid level when compared to control. © 2002, Japan Oil Chemists' Society. All rights reserved.