Surface of corn starch films was modified through esterification using octenyl succinic anhydride as reactant. Physical properties of the films, moisture absorption, and water contact angle were measured to characterize the effect of the Surface esterification modification. The influences of the concentration of alkaline aqueous solution for activating starch, reaction temperature, and time were investigated. It was found that the pretreatments with 1.0% or 2.0% NaOH aqueous solution and reacting at 35 degrees C for 6 h gave rise to films possessing higher water contact angle, lower equilibrium moisture content, and moisture absorption rate at 95% relative humidity (RH). After the surface esterification modification, the equilibrium moisture content of the starch film decreased up to 29% at 95% RH and the surface water contact angle of the film increased up to 83%. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 114: 940-947, 2009