Cottonseed oil is one of the common edible oils in our country, whose fatty acid composition endows the oil with good frying stability and shortening property, the fried foods with good appearance and rich in nutrition. During the frying process, water and oxygen could cause the hydrolysis, oxidation, polymerization, cracking and a series of complex chemical reactions in oils. Therefore, the physical and chemical indicators of the oils would be changed.The acid value, peroxide value, carbonyl value, p-anisidine value and the content of polar substances of the cottonseed oil were determined during the process of frying chicken. The result showed that the variation of polar substances, acid value, carbonyl value and conductivity was linear with the frying time, which indicated the change of the cottonseed oil quality.