Abstract: The effects of nettle (Urtica diocia L.), containing natural antioxidants, on chemical properties of rainbow trout (Oncorynchus mykiss) fillets were investigated. Thiobarbituric acid reactive substance (TBARS), total antioxidant activity, total volatile bases nitrogen (TVB-N) and pH values were measured from rainbow trout fillets treated with nettle at three concentrations (0.4, 0.8 and 1.6), without nettle as control and 0.8% propyl gallate (positive control) during 9 days of storage at 4±1 °C. The storage time and antioxidant treatment caused significant (p<0.05) changes in TBARS, total antioxidant activity, TVB-N and pH values. TBARS values in fillets of control group exceeded the acceptable level (20 μmol kg-1) on the 5th day. However, fillets treated with nettle at three concentrations and propyl gallate did not reach this degree during the experimental period. The fillets treated with 0.4% of nettle exhibited most effective and powerful antioxidant activity. The antioxidant activity of samples decreased with increasing nettle concentrations. However, the samples treated with 0.4 and 0.8% of nettle showed higher antioxidant activities than that 0.8% of propyl gallate. TVB-N values in fillets of control group reach above 25 mg/100 g on the 3rd day. However, nettle and propyl gallate groups were reached above this level on 5th day. Considering present data, it was concluded that using nettle containing natural antioxidants might cause a distinct beneficial reduction in lipid oxidation and extend storage time of aerobically packaged rainbow trout fillets.