The surface tensions of 6- O -hexanoyl, octanoyl, decanoyl and dodecanoyl L-ascorbates, which were synthesized via the immobilized-lipase-catalyzed condensation of ascorbic acid and the corresponding fatty acids in acetonitrile, were measured at 25°C by the Wilhelmy method at their various concentrations, and the critical micelle concentration, CMC, and the residual area per molecule, a , were evaluated for each acyl ascorbate. The CMC was lower for the ascorbate with a longer aryl chain, while the a values were ca . 0.30 nm² for all the acyl ascorbates.