Interferometric microscopy was used to observe the initial stage of the crystal growth of an organic charge transfer salt (DMe-DCNQI)(2)Cu by electrochemical reaction. It was found that concentric patterns started to appear after applying the potential difference between the electrodes. Bright rings of the concentric pattern moved outward for about 15 s and slowed down the movement after the period. It shows the change in the solution concentration just after the nucleation. (C) 2003 Elsevier Science B.V. All rights reserved.