This study reports the novel synthesis of nano-sized cellular Fe3O4 thin film with high degrees of crystallinity and purity using an electrochemical deposition of green rust 2 (GR2) and its further oxidation. This technique is applicable to substrates with large surface areas of a few square centimeters or more without the aid of templates, high temperature, vacuum, or post-treatment. Cellular Fe3O4 thin film showed a rectangular cyclic voltammogram indicative of a typical capacitive behavior in 1 M Na2SO4 solution and showed a specific capacitance as high as 105 F/g, thereby demonstrating its promising potential as an electrode material for supercapacitors. (C) 2005 The Electrochemical Society.