This study was aimed to evaluate the effects of dietary supplementation of different extracts of Origanum minutiflorum O. Schwarz et. P.H. Davis on nonspecific immune system and antioxidant parameters in rainbow trout. The rainbow trouts were given feeds containing crude plant, lyophilized water extract, and essential oils at three different concentrations for 8 weeks. The nonspecific immune system, antioxidant, and weight performance parameters were evaluated at the end of feeding period. The respiratory burst, lysozyme and phagocytic activities increased significantly as an indicator of immunostimulant activity in the experiment groups fed 1000 and 500 mg/kg essential oil. The feed containing 1000 and 500 mg/kg lyophilized extract was found to increase respiratory burst and phagocytic activities. The malondialdehyde levels decreased significantly in the experiment groups fed all the essential oils concentrations and 1000 mg/kg lyophilized extract. The superoxide dismutase activity in the liver increased in 1000 mg/kg lyophilized extract and 1000 mg/kg essential oil groups; glutathione peroxidase increased in groups fed all the essential oils and lyophilized extract; glutathione S-transferase activity showed no change, and the catalase activity increased statistically in 1000 mg/kg essential oil and 1000 mg/kg lyophilized extract groups. The findings of this study suggested that O. minutfflorum could be used in the feed for the rainbow trout considering that the plant extract and essential oils of the plant had positive effects on the nonspecific immune system and antioxidant activity.