This study was undertaken to investigate the impact of replacement of fishmeal (FM) with soybean meal (SBM) in diets of rainbow trout (Oncorhynchus mykiss). A total of 600 rainbow trout, with an initial mean body weight of 15.92 ± 0.34 g, were distributed randomly into twelve experimental tanks (50 fish per tank). Four isoenergetic and isonitrogenous feed diets were allocated to each treatment, with three replicates/treatment (12 fish/replicate). FM and fish oil were replaced gradually by SBM in the four diets. The inclusion of SBM in diets 1-4 was at the following respective levels of 0% (control), 29%, 35% and 51%. Growth performance of fish fed diet 4 was significantly lower than that of fish fed the other diets (P<0.05). The dietary inclusion of SBM up to level of 35% did not affect the blood biochemical parameters of rainbow trout, and was associated with acceptable growth performance. In conclusion, the SBM can be included in diet of Oncorhynchus mykiss at 35%, while keeping the level of FM and fish oil at 51%, and 1%, respectively.