Three vegetable oils with different unsaturation degree, namely, unflower seed oil, peanut oil and rapeseed oil, were selected to evaluate the formation of polar compounds and their distribution during frying and thermoxidation. It was found that the levels of polar compounds mainly depended on oil unsaturation degree with same frying conditions. Relative molecular weights of triglyceride oligomers, triglyceride dimmers and oxidised triglyceride monomers were also detected by high performance sizeexclusion chromatography.