Propolis (bee glue) is a resinous material gathered by honeybees from the buds and bark of trees and plants. Its chemical composition includes more than 300 compounds and it has various biological activities, namely anticancer, antioxidant, anti-inflammatory, antibiotic, antifungal and antihepatotoxic. Because of the importance of rainbow trout ( Oncorhynchus mykiss ) in Iranian aquaculture and the unknown biological characteristics of propolis of Iran , this study was conducted to evaluate the effects of orally administered propolis ethanolic extract on growth parameters (final weight, survival, specific growth rate, weight gain percent, food conversion ratio, hepatosomatic index, viscerosomatic index, protein productive value and protein efficiency ratio), body composition (humidity, protein and lipid), health indicators (blood indices Hb and Hct and serum biochemical parameters GOT, GPT, ALP, LDH, TP, Alb, Glb, Alb :Glb ratio, CHOL, TG, HDL and LDL) and immune system (NBT test) of rainbow trout ( O. mykiss ). Propolis was dissolved in ethanol (1 : 9 weight/weight) and added to diets (based on solid propolis weight). Juvenile rainbow trout (mean initial weight 14 g) were fed on experimental diets (3% of biomass per day) supplemented with 0(control), 0.5, 1.5, 4.5 and 9 g propolis/Kg diet for 8 weeks (four replicate tanks for each treatment). Results did not show significant differences between growth parameters within different treatments (P 0.05), however the increasing of propolis concenteration level results in increasing of Hb and Hct. Hb and Hct values were significantly higher in groups receiving 4.5 and 9 g propolis/Kg diet than that of control group (p 0.05). Although there were no significant differences between serum biochemical parameters, only the Alb : Glb ratio was significantly higher in group receiving 4.5 g propolis/Kg diet than that of control group (p 0.05). The present study showed that the administration of 9 g propolis/Kg diet resulted in a significant increase in the NBT index (positive blood neutrophils) of experimental fish after 8 weeks (P 0.01), there is also an increasing trend in NBT index with the level of propolis. It can be concluded that administration of ethanolic extract of propolis in mentioned levels do not have any effects on growth and health of experimental fish, also this compound can stimulate immune system of fish. Keywords : Propolis, Rainbow trout, Health indicators, Blood indices, Serum biochemistry, Immune system, NBT