Herein, we report a facile synthesis of iron oxide nanopatticles by a hydrothermal route. The X-ray diffraction analysis confirms that these nanoparticles are of pure magnetite (Fe3O4) phase. Further, the morphology and average particle size were investigated using scanning electron microscopy. The average particle size of these nanoparticles was observed to be similar to 65 nm. The magnetic measurement reveals the ferromagnetic nature of the synthesized Fe3O4 nanoparticles at room temperature. The coercivity and remanence magnetization were observed to be 98 Oe and 0.51 mu(B)/molecule, respectively. Fe3O4 nanoparticles showed a sharp transition (Verwey transition) around 120 K in M vs. T measurements. The observation of the Verwey transition indicates the high quality and phase purity of the synthesized Fe3O4. Moreover, the Fe3O4 nanoparticles were electrochemically characterized for their potential application as an electrode for ultra-capacitors. The specific capacitance of 97 F/g at the current of 1 mA was observed with excellent cyclic stability. The present facile synthesis method could be a potential approach for fabrication of ultra-capacitors using cheap and environment friendly ferromagnetic iron oxide nanoparticles for high performance energy materials. (C) 2014 Elsevier B.V. All rights reserved.