Abstract: An effective way to improve the oxidative stability of biodiesel is selective hydrogenation of the polyunsaturated fatty acid methyl esters in biodiesel.Selective hydrogenation of fatty acid methyl esters was investigated using deep eutectic solvent as a solvent,and PdCl₂ as catalyst.If the iodine value (76 g/100 g) was taken as evaluation criterion when methyl linoleate was completely hydrogenated to methyl oleate,the optimum reaction conditions were as follows:DES synthesized with choline chloride and urea as solvent,molar ratio of palladium chloride to sunflower seed oil fatty acid methyl ester (1:20),reaction temperature (60℃),rotation rate of 600 r/min.Iodine value of hydrogenated products had the lowest value of 87 g/100 g under this condition.Methyl oleate content was 74.19%,methyl linoleate content was 13.44%,and there was little change in saturated fatty acid methyl ester content nearly in hydrogenated fatty acid methyl esters.