The surface tension of aqueous solution of arachidonic acid (AA) was measured with a Du Nouy tensiometer at pH 7.80 and various temperatures, and the effect of temperature on the surface properties of AA was investigated. The value of critical micelle concentration (cmc) of AA increased and the surface tension at the cmc, γcmc, decreased as the temperature was raised from 30 to 60°C. The Langmuir constant k concerning the strength of adsorption decreased, the saturated adsorption ammount of AA, Γ∞, at the air-water interface decreased, and the area occupied by an AA molecule at the saturated adsorption, A∞, increased as the temperature was raised. The standard free energy for the adsorption, ΔGad, was of negative value, and the absolute value |ΔGad| became larger as the temperature was raised because of the negative value of the standard enthalpy change ΔHad and the positive value of the standard entropy change ΔSad. The standard free energy of micellization, ΔGm, was of negative value, and it was similarly found that |ΔGm|became larger as the temperature was raised because of the negative value of the standard enthalpy change ΔHm and the positive value of the standard entropy change ΔSm.