Abstract: To improve content of physiologically active substances EPA and DHA from fish oil, using fish oil ethyl esters as materials and mixing them with saturated urea ethanol solvent, saturated fatty acid esters will be clathrated by urea and are then separated away in crystal forms. With the increasing of the mole ratio between urea and fish oil fatty acid ethyl esters, or with the decreasing of the crystallization temperature, products which contain EPA and DHA over 70 % can be easily prepared.