Prussian blue, Fe[Fe(CN)(6)] currently attracts a huge attention as a promising material in the application of large-scale energy storage because of its cost-effective and environmental friendly material. Besides, open framework structure and stability are the main causes for PB performance. In this study, effects of sodium cation insertion/deinsertion toward the structural and electronic properties were analyzed. The use of Hubbard U method successfully delivered a good approximation on electronic properties of the transition-metal ions in PB. The calculated band gap of 1.84 eV was in good agreement with theoretical and experimental results. Upon the insertion of the sodium cation, volume of the cathode material expanded between 2% and 4% showing that this cathode material has good cycle retention. From partial density of states, Fe 3d dominated the conduction and valence band. Furthermore, the redox reaction mechanism of Prussian blue can also be depicted. The voltage obtained from energy calculation for the first and second insertion of cation was 3.32 and 3.42 V, respectively.