This research was realized in two periods, one pre experimental in 112 days and other experimental in 43 days, aiming to evaluate the effects of vitamin C and lipid on differential leukocyte counts of fish submitted to temperature stress. Leukocyte cells were evaluated at the beginning and the end of the experiment. The experiment used a 2 x 3 factorial design with vitamin C (300.0; 600.0 and 1,200.0 mg/kg diet) and lipid levels (8.0 and 12.0%) with four replicates, plus absence of nutrient test and 6.0% lipids and 125.0 mg/kg vitamin C diet. Diets were formulated to contain 32.0% of DP. Fish were stocked into 24 40-L aquaria at a density of two fish/aquarium, with weight of 105.13 ± 19.71 g. Water temperature was kept at 18.0°C during 25 days and at 15.0°C during 11. Low temperature determine a decrease on leucocytes and lymphocytes and an increase on neutrophils and monocytes. There was a significant interaction between phase x vitamin C and phase x lipid. It was concluded that v itamin C and lipid supplementation improve immune response; low temperature determine a decrease in fish resistance; levels of vitamin C supplementation above the requirement and 8.0 and 12.0% of lipid on diet determine a better resistance. KEY WORDS: Ascorbic acid, low temperature, Oreochromis niloticus , resistance, white blood cell.