Abstract: Using 5 yearsold grafted trees of Citrus ichangensis, Bendizao Tangering (C.regiculata), and Jincheng sweet orange (C.sinensis) to study their cold resistance and their fluctuation of the fatty acid composition in the leaf lipids in winter, experimental results showed that in the average diurnal temperature of 24℃, citrus leaves began to accumulate unsaturated fatty acids. When temperature droped from 13℃ to 7℃, the content of the unsaturated fatty acids in the citrus leaves had a rapid increace. The amount of unsaturated fatty acid in winter was about 60% higher than that in the summer. During spring, the amount of unsaturated fatty acids was decreasing, while that of saturated fatty acids was increasing. It seemed that there was a certain correlation between the unsaturated fatty aeids and cold resistance in the citrus species. The amount of unsaturated fatty aeids of these species in the leaves and seeds were coindental correlated with the cold resistance of the species.