The electrochemical oxidation of 2,5-dihydroxybenzoic acid （1） has been studied in the presence of 1,3- cyclopentadiene （2） as a diene in water/ethanol （40/60, v/v） mixture using cyclic voltammetry and controlled-potential coulometry. A plausible mechanism for the oxidation of 1 in the presence of 2 is presented. Compound 1 was converted into bis-adduct 5 via electrooxidation, Diels-Alder reaction of 2 to anodically generated 3,6-dioxocyclohexa-l,4-dienecarboxylic acid （lox）, decarboxylation reaction, electrooxidation and Diels-Alder reaction. The electrochemical synthesis of 5 was performed in a one- pot reaction, without toxic reagents, at a carbon electrode in a simple cell using an environmentally friendlv method.