A reaction of maleic anhydride with epoxy-dian resins in methyl ethyl ketene was investigated. It was shown by potentiometric titration that the resulting maleic esters are stable to hydrolysis in acid and weakly acid organic solutions. This reaction can be used for the quantitative determination of hydroxyl groups in epoxy resins. Epoxy groups do not interfere with the formation of maleic esters under the conditions of determination. The optimal reaction conditions were found. The reaction kinetic was investigated, the reaction rate constants were determined at various temperatures, and the activation energy was found. The value of the activation energy indicates that the reaction is characterized by a low potential barrier. © 2001 MAIK "Nauka/Interperiodica".