Deltamethrin is a commonly used pyrethroid pesticide. Vitamin E is a antioxidant that plays an important role in protecting cells against toxicity by inactivating free radicals generated following pesticides exposure. Therefore, in the present study, it was evaluated whether deltamethrin induced changes on the fatty acid composition of phospholipid in gill and liver tissues in Oreochromis niloticus and, the possible protective effect of vitamin E against deltamethrin was determined. Fish was fed with no pesticide+control diet, no pesticide+vitamin E-supplemented diet, 1.45 mu g/l deltamethrin+control diet, 1.45 mu g/l deltamethrin+vitamin E-supplemented diet for twenty days. Pesticide and diet quality made an impact on the fatty acid composition of phospholipid. In treatments of deltamethrin, group fed with control diet showed much greater damage in comparison with group fed with vitamin E supplemented diet. The results indicated that the deltamethrin led to an increase in the percentages of total SFAs (saturated fatty acids) and total MUFAs (monounsaturated fatty acids) and a decrease in total PUFAs (polyunsaturated fatty acids) in the gill tissues. However, coadministration of deltamethrin and vitamin E showed decrease in the percentages of saturated fatty acids and increase in the percentages of polyunsaturated fatty acids in the gill tissues. In group fed with control diet, deltamethrin led to a decrease in the percentage of SFAs and a increase in total MUFAs in the liver. Coadministration of deltamethrin and vitamin E showed increase in the percentages of polyunsaturated fatty acids in the liver tissues. These results have demonstrated that administration of vitamin E along with deltamethrin decreases the peroxidation of unsaturated fatty acids and thus protects the cell membranes. (C) 2012 Elsevier Inc. All rights reserved.