Cobalt ferrite nano-powder have been obtained through a hydrothermal method with 2:1 molar ratio of Fe:Co without using any surfactant. X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) were used to consider the structural and morphological properties of CoFe2O4 nano-particles. Also, EDAX spectroscopy applied to evaluate the chemical composition. Results demonstrated that 15 hr hydrothermal processing was enough. In the hydrothermal period of reaction more than 15 hr (21 hr) Fe2O3 sub-phase was identified which this could be due to instability of CoFe2O4 at supercritical condition. The average particle size and the percentage of crystallinity for single phase sample were calculated 34.7 nm and 98%, respectively.