Electrochemical oxidation of acetaminophen (paracetamol) has been studied in various pHs using cyclic voltammetry and controlled-potential coulometry. The results indicate that electrochemically generated N-acetyl-p-benzoquinone-imine (NAPQI) participates in different type reactions based on solution's pH. It is hydrolyzed in strong acidic media and hydroxylated in strong alkaline media and also, it is dimerized in intermediate pHs. Furthermore, in this work, a simple method for electrochemical synthesis of acetaminophen's dimer is described. In addition, in various pHs, based on related mechanism, theobserved homogeneous rate constants (k(obs)) of hydrolysis, hydroxylation and dimerization reactions were estimated by comparing the experimental cyclic voltammetric responses with the digital-simulated results. The most amounts of k(obs) are calculated in pHs less than 2 and more than 9. In this study, the least observed homogeneous rate constant (k(obs)) belongs to pHs 5.0 and 9.0. (C) 2009 Elsevier Ltd. All rights reserved.