The objective of this work is to investigate Fe3O4/C composite as an electrochemical capacitor. Fe3O4 nanoparticles were synthesized by oxidation of iron in water using either constant direct current (CDC) or pulse direct current (PDC). Fe3O4/C composite was prepared by two methods: (1) the nanoparticles were mixed with sucrose and carbonized at 500 C under the mixture of 5% H-2 in N-2, and (2) the nanoparticles were mixed with carbon black. The electrochemical performance of the composite was evaluated by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The diameters of Fe3O4 particles obtained using CDC and PDC methods were approximately 18.7 nm and 20 nm, respectively. The specific surface area of composite with method (1) using PDC was 112.93 m(2)/g and using CDC was 111.58 m(2)/g, and method (2) using PDC was approximately 48.345 m(2)/g and using CDC was 40.77 m2/g. EIS analysis showed that the conductivity of the composite prepared by method (1) using CDC lower than that using PDC and method (2) gave the same result. The lower specific surface area gave better conductivity. Cyclic voltammetry analysis for some cycles showed that the area under the anodic-cathodic curve for the both methods (1) and (2) using PDC or CDC did not give the good result and for method (2) gave the same area. This is affected by diameter particles of composite.