Surface tensions of aqueous solution of eicosapolyenoic acids (EA) with 2 approximately 5 double bonds were measured by use of a Du Nouy tensiometer at pH 7.80 and 25-degrees-C, and the effects of double bond on the surface properties of EA were investigated. The value of critical micelle concentration of EA increased twofold with increasing number of double bonds. The free energy for the adsorption per double bond at the air-water interface was estimated as 2.47 kj (double bond)-1, and the negative value of free energy for the adsorption of EA molecule decreased with increasing number of double bonds.