The present experiment was conducted to describe the effects on histology (experiment 1) and nutrient digestibility (experiment 2) of rainbow trout fed with diet containing O. onites oil. Diets were prepared with supplemented in different concentrate (0, 0.125, 1.5, 2.5, 3.0 ml kg(-1)) of O. onites oil. A total of 1050 trout (body weight 26.05 +/- 0.15 g) were randomly stocked into 15 tanks. The experiments were done in triplicate. In the experiment 1, rainbow trout were fed during 90 day for histology analysis. Five fish samples from per tank were taken at the end of the experiment. Liver and kidney histopathology of the control fish showed a normal histological architect without indication of any deformity. Slightly necrosis or degeneration were observed in liver and kidney samples of fish fed with high level of O. onites oil in diets. In the experiment 2, nutrient digestibility study was conducted for 2 week in following of the histology experiment. Nutrient digestibility was determined using 0.5 % Cr2O3 as an indicator to diet. Feces were collected by siphon from bottom of tanks during 2 week. The end of the experiment, dry matter, protein and lipid digestibility did not affect with supplemented in different concentrate of O. onites oil to trout diet.