Electrochemical oxidation of rosmarinic acid (RA) in aqueous solutions has been studied using cyclic voltammetry, linear sweep voltammetry and differential pulse voltammetry. RA (1) has two catechol rings, and the electrochemical study of it shows two oxidation-reduction peaks (E r E r mechanism). In the first step oxidation RA (1) converted to OX1-1, and in the second step of oxidation the produced OX(1-1 )oxidized to OX2 . Two possible structures were designed for the first step of oxidation and optimized at the B3LYP/6-311 G (d, p) level of theory. To confirm the results, the oxidation potential of RA (1) was compared with some catechol species at pH = 0.0. Plotted diagram of the oxidation potential versus Delta G(tot) showed a good correlation between the electrochemical oxidation potential (E-pA0) and calculated Delta G(tot )of electrochemical oxidation of studied species. The voltammetric study in the basic solutions shows a dimerization reaction after electron transfer process. Analysis of the voltammograms shows a partially adsorption behavior in the electrochemical oxidation of RA (1). Also, pKa of RA (1) was determined by the use of acid-base titration and effect of deprotonation of RA (1) on voltammograms was studied. (C) 2018 The Electrochemical Society.