In the world the tendency to fish consumption in order to provide food and also obtain to its beneficial effects on human health is increasing. If prepared foods be frozen, not only their shelf-life would be longer, but also different methods such as oven or microwave can be used to make food ready to use in a short time. Nowadays cooking–freezing and reheating (CFR) method is considered as a suitable alternative to conventional cooking in which food is cooked, frozen and heated shortly before eating. There are different methods that could prevent the lipid oxidation in food products. The use of plant extracts is one of the methods that prevent lipid oxidation and extend the shelf-life of food products due to its antioxidant and antimicrobial activities. In the current study Green back mullet fish were prepared by two methods, frying and oven baking and then transferred to the freezer (-18?C) for 5 months. In defined intervals, samples were reheated using oven and microwave and oil physiochemical characteristic and fatty acid profile of treated and row fish were compared and analyzed. Moreover, the effect of fennel extract in the oxidation prevention of fish oil was studied. The results revealed that the moisture content of the samples decreased during baking, while the amount of protein and ash increased. Fried sample due to the oil absorption during cooking had the highest fat content (8.6%). Frying method in comparison to oven baking had less effect on the chemical properties of the fish. Oil at the end of storage time acid value (AV), peroxide value (PV) and TBA were 3.5%, 3.8 meqO2/Kgoil and 0.4 mgMDA/Kgoil, respectively which were much less than the values in the oven-baked sample. Among reheating methods, there was no significant different in AV, PV and TBA which means that both of oven and microwave methods can be used for reheating frozen fish. Using fennel extract in oven baking successfully could prevent fish oil oxidation during 5 month of storage. However, this extract could not have the expected antioxidant effect in frying method. The omega-6 to omega-3 fatty acids ratio in the oven baking did not differ with raw sample while this ratio in fried samples due to the oil absorption increased dramatically. Finally, it can be said that fennel extract due to its antioxidant effect can increase the shelf life of food products which are sensitive to oxidation although use of higher concentrations of this plant extract may improve its functional properties. Keywords : Fennel extract, Frynig, Green back mullet fish, Oven, Reheating,