A 60-day feeding study with rainbow trout, Oncorhynchus mykiss, was conducted to determine the effects of replacement of fish oil (FO) by unrefined peanut oil (PO) on growth performance, feed utilization, body composition, fatty acid composition and serum biochemical and haematological parameters. Rainbow trouts (51.60 +/- 0.75g) were fed five experimental diets formulated by replacing dietary FO with PO at levels of level 0 (PO0), 1/4 (PO25), 1/2 (PO50), 3/4 (PO75) and 4/4 (PO100), respectively. As a result, the best growth performance was observed in fish fed with PO0 and PO50 diet. No significant differences were detected among the groups in terms of body compositions. Fatty acid profiles of the fish fillets reflected the fatty acid profiles of the feeds that the fishes were fed with. In this study, the haematological parameters detected that there were no significant differences compared to the control group, whereas the serum biochemical parameters generally worsened as the ratio of peanut oil in the ration exceeded half of fish oil. As a conclusion, the results of the study suggested that the unrefined peanut oil could be used as a replacer of fish oil in diets for rainbow trout.