: Dr Hongyun Tai2024-12-152024-12-15https://dspace.academy.edu.ly/handle/123456789/8821- Introduction Food is the primary source of nourishment and strength of the body to contain energy sources and nutrition such as carbohydrates, vitamins, fats and proteins. Fat is an important of the diet to maintain good health because of the high energy value of unsaturated fatty acids; they are essential for the healthy development of living organisms.1 In addition to being carriers of cholesterol and the formation of cell walls.1 Fat/oils are commonly used in cooking. Plant oils are widely used in food products and are increasingly applied in frying operations. Where the consumption of fried foods in the world, for several reasons, including: speed of transfer of heat by oil and thus reduceThree types of oils (sunflower oil, corn oil and olive oil) were heated under different temperatures (100, 150, 200, 250, 300 0C) for 1 and 5 hours without food, also heated to 250 0C in presence of pieces of potato. The deteriorations reflected by the changes in chemical structures of the oils after heating were studied using 1H nuclear magnetic resonance( 1H-NMR) and Fourier transform infrared spectroscopy (FTIR) which can detect the formation of aldehydes and the degradation of acyl groups, as well as the formation of mono- and di-glycerides in the presence of air and humidity. The differences were found between the behaviour of different oils used under identical conditions. The temperatures at which physical changes were observed, such as smoke point and discoloration have been recordedAnalysis of changes in chemical structures of plant oils after heating process