Abstract: The effects of vitamin E were studied in fingerlings rainbow trout (Oncorhynchus mykiss) kept at two different densities. Fingerlings (initial weight of 2.1±0.1 g) were reared in triplicate groups in fiberglass tanks at densities of 400 and 800 m3. The fish were fed with 4 diets containing different levels of vitamin E (0, 100, 200 and 1000 mg vitamin E kg-1diet) for 9 weeks. The at end of feeding experiment fish were exposed to different temperatures (24, 26 and 28°C) and evaluate survival. The growth performance in fish fed diets containing different levels of vitamin E (100, 200 and 1000 mg kg-1 diet) was significantly (p<0.05) higher than those fed diet without vitamin E. Levels of vitamin E significantly (p<0.05) affected the hematocrit, hemoglobin, Red Blood Cells (RBC) count, Mean Corpuscular Hemoglobin (MCH) and eosinophil in rainbow trout. However, it did not change Mean Corpuscular Hemoglobin Concentration (MCHC), lymphocyte and monocyte values. Stocking density had significant effect on eosinophil count only. Survival of the treated fish was significantly (p<0.05) higher than the control in response to heat stress. The highest effects of vitamin E was at level of 200 mg kg-1 and a density of 400 pieces m-3.