This study was conducted to examine the effects of dietary Aloe vera supplement on growth parameters, hematological indices, non-specific immune stimulate and acute stress response of fingerling rainbow trout. Four experimental diets, supplemented with the Aloe vera gel powder at ratio of 0, 1, 2 and 5 g per kilogram of food, corresponding to 0, 0.1, 0.25, and0.5% of daily ration were assayed on experimental fish for 6 weeks. Three hundred fish (mean weight of 20 ± 0.01 g) were acclimatized to the laboratory conditions for two weeks, and then randomly divided into four groups of 25 fish with three replicates. Each group was kept in a 120 L fiberglass tank in a semi-recirculated system for six weeks. At the end of feeding trial, growth parameters, hematological parameters (hematocrit, hemoglobin, WBC, RBC, lymphocyte, monocyte, eosinophil, basophil, and neutrophil count), lysozyme activity, total protein, serum proteins (globulin, albumin), glucose and cortisol levels, Na + , Cl - , and survival rate were measured. Thereafter 2 groups with 30 fish from each treatment were randomly subjected to acute temperature and salinity stress, increasing from 12 to 20 ? C and 0 to 11 ppt respectively. After an hour temperature and salinity levels were reduced to initial level. Blood samples from stressed fish were taken 1, 3, 6, 12 and 24 hours after termination of stress test. Modulatory effects of Aloe vera on acute stress response (cortisol, glucose, hematocrit, hemoglobin, Na + , Cl - and lysozyme activity) were measured. Results indicated that fish fed 0.1 and 0.25% aloe had the highest final body weight (P 0.05), whereas WG, FCR and SGR did not show significant difference among different groups. Aloe level at 0.1, 0.25 and 0.5% of diet significantly increased the number of WBC, RBC, Hct and Hb in rainbow trout. Eosinophil percentage also increased remarkably group of fish received 0.25% aloe, compared to other treatments. The lysozyme activity in serum were found to be significantly (P 0.05) greater in fish fed Aloe vera supplement at 0.25%. Fish fed with 0.5% aloe had higher albumin compared to other groups (P 0.05). Highest survival rate of 100% was recorded at 0.5 % Aloe group followed by 98.6 % at 0.1 and 0.25% Aloe treatments. Lowest survival rates were observed in fish with no Aloe vera in diet. After imposing acute stress, plasma cortisol and glucose levels, lysozyme activity, hematocrit and hemoglubin levels of fish fed supplemented Aloe vera diet showed significantly lower changes than fish fed the 0% Aloe vera diet (P 0.05). Based on our findings it can be concluded that the addition of Aloe vera into the diet could enhance resistance against temperature and salinity stress and would increase the non-specific immune of fingerling rainbow trout. However, in order to consider the effects of Aloe vera on the growth and suggesting certain dosage of that, more investigation is required. Key words: Aloe vera , growth parameters, hematology indeces, acute stress, survival rate, rainbow trout .