In this study, the effects of frying, oven-baking, barbecuing, and smoking on the proximate composition and lipid quality of trout (Onchorhynchus mykiss) were studied. The proximate compositions were affected significantly by all cooking methods. An increase in the lipid content and a decrease in the moisture content were observed in all the cooking methods. A decrease in the protein content was found in barbecued and smoked samples, but not in fried or oven-baked, on dry-weight basis. Regarding the lipid quality, the free fatty acids (FFA, grams of oleic acid per 100-g lipid), peroxide values (POV, meq active oxygen per kg lipid), and thiobarbituric acid values (TBA, mg malonaldehydeper kg fish muscle) were analysed. The FFA contents in fresh, fried, oven-baked, barbecued and smoked trout on wet-weight basis were found to be 8.76, 0.76, 5.05, 0.81, and 9.44-g oleic acid per 100-g lipid, respectively. POV in fried, oven-baked, and barbecued samples increased significantly, while POV in smoked samples decreased significantly. An increase was observed in the TBA value in trout cooked with all methods. The results of this experiment showed that heating accelerates lipid oxidation.