BACKGROUND: The immunostimulating effect of Aloe vera in mammals has been documented, but few works were done on effect of A. vera on fish health and immune responses. OBJECTIVES: In this study the effect of oral administration of A. vera on growth indices, hematological parameters and immune responses of rainbow trout were investigated. METHODS: One thousand five hundred rainbow trout fingerling (20 ± 2 g, Mean ± SD) were divided into five groups, each in triplicate, in farm scale. Group 1 were adopted as control and fed with non-supplemented feed, groups 2 to 5 were fed with diet supplemented by 0.05%, 0.1%, 0.2% and 0.5% A. vera extract respectivly for 60 days. Growth indices (SGR, FCR, PWG, FER, PER and CF) calculated in day 30 and 60. Blood samples were taken in day 60 and hematological parameters including: PCV, Hb, RBC, WBC, MCH, MCV, MCHC as well as immunological parameters including: Lysozyme and serum bactericidal activity, serum total protein and globulin were compared among the groups. RESULTS: Results showed that all calculated growth indices (except CF) and all mentioned immunological parameters were significantly increased in fish fed with 0.1% and 0.2% A. vera supplemented food (G3 and G4) compare to control group (P < 0.05). Hematological parameters, HB, RBC, WBC and PCV showed a significant enhancement in G3 and G4 compare to control (P<0.05), but MCV, MCH and MCHC showed no significant changes (P > 0.05). CONCLUSIONS: It can be concluded that oral administration of 0.1% and 0. 2% A. vera crud extract in food (G3 and G4) can improved growth indices, stimulate non-specific immune responces and affect some hematological parameters positively in rainbow trout.