Cyclic voltammetry results as a diagnostic technique for electrochemical oxidation of 4-(4-R-phenyl)-1,2,4-triazolidine-3,5-diones (1-5) are reported and discussed. The results indicate that the electrochemically generated 4-(4-R-phenyl)-4H-1,2,4-triazole-3,5-diones (1ox-5ox) are unstable and participate in oxidative ring cleavage. In this study, the effect of different parameters such as pH, 4-phenylurazole concentration, solvent, temperature, substitute effect and time window of chosen electrochemical method have been studied. Also, the transfer coefficient, alpha a exchange current density, J(0), the formal potential, E-0' and diffusion coefficient, D, of 4-phenylurazole (1) have been calculated. In addition, the observed homogeneous rate constants of oxidative ring cleavage of 4-phenylurazole derivatives were estimated by comparing the experimental cyclic voltammetric responses with digital simulated results. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.111206jes] All rights reserved.