Phenomenological coefficient was used as a quantitative factor to examine cyclability of an electrochemical redox system. The insertion/extraction of potassium ions into/from solid film of Prussian blue (PB) was chosen as a typical example with a known electron-ion hopping mechanism. The phenomenological coefficient for the flux of counter ion (or equivalently electron) at various cycles were estimated based on an approach using different techniques, viz. cyclic voltammetry and simple conductivity measurement. The advantage of phenomenological coefficient in comparison with peak current for the investigation of cyclability of an electrochemical system was described. (C) 2003 Elsevier B.V. All rights reserved.