In this work, we present the results of a kinetic study of the surface modification of the carboxyl group of poly(ethylene-co-acrylic acid) into acyl chloride. Reaction temperature and time, concentration of the reactants, kind of agitation have been changed in order to understand their effect on the conversion. A study on the penetration of the reaction inside the sample bulk was also performed. The results indicate that, when short reaction times are adopted, the reaction limits to the outer layers of the samples and, in this case, on increasing the temperature, the concentration of the reactants and the stirring allows having a faster kinetic. At longer reaction times, the reaction penetrates deep inside the sample (several tens of microns) and the influence of the above mentioned variables on the kinetic is very low. The results, obtained by direct FTIR, ATR-FTIR, SEM-EDX and contact angle measurements, were confirmed and corroborated by theoretical estimations. (C) 2009 Elsevier Ltd. All rights reserved.