A novel all-organic redox flow battery employing 2,2,6,6-tetramethyl-1-piperidinyloxy/NaClO4/acetonitrile and N-Methyl-phthalimide/NaClO4/acetonitrile as catholyte and anolyte, respectively, is investigated by electrochemical measurements. The quasi-reversible and stable redox reactions are tested by cycle voltammetry. The diffusion coefficient of 0.02 M 2,2,6,6-tetramethyl-1-piperidinyloxy and 0.02 M N-Methylphthalimide in the supporting electrolyte are all in the range of 0.7-1.1 x 10(-5) cm(2).s(-1) at room temperature. Stable charge-discharge curves and high coulombic efficiency (90%) for the first 20 cycles are obtained through charge-discharge test. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.012112esl] All rights reserved.