The kinetics of esterification of 7-theophyllineacetic acid with diethylene glycol monomethyl ether in the presence of dicyclohexylcarbodiimide and 4-dimethylaminopyridine as catalyst was studied. According to the known mechanism, besides the main process, the side-reaction of intramolecular rearrangement with formation of pharmacologically active N-acylurea occurs. The course of the main and the side-process was monitored by RP-HPLC with UV-detection. For that purpose, quantification of both ester and N-acylurea in the reaction mixture was performed. Influence of the concentration of the reactants (acid, alcohol and catalyst) on the progress of esterification and preparation of the by-product was investigated. Based on the obtained results, the reaction conditions leading to maximal yield of the ester and N-acylurea are proposed. The possibility of turning esterification to the synthesis of the side-product was also found. Reactions of the preparation of both the ester and N-acylurea were found to follow first-order kinetics. The rate constants of both processes were estimated.