The Fe3+/Fe2+redox electrolyte for use in polyaniline/tin oxide (PANI/SnO2) supercapacitors was reported. The influences of redox electrolyte based on different Fe3+/Fe2+ion pair concentrations in 1 mol/L H2SO4solution on the pseudocapacitive behaviors of PANI/SnO2supercapacitor were investigated. The electrochemical properties of the supercapacitor were studied by cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy (EIS) techniques. It is found that the performance of the supercapacitor is the best when the Fe3+/Fe2+concentration is 0.4 mol/L and its initial specific capacitance is 1172 F/g at an applied current density of 1 A/g. The long-term cycling experiment shows good stability with the retention of initial capacitance values of 88% after 2000 galvanostatic cycles. The experimental results testify that using Fe3+/Fe2+redox electrolyte has a good prospect for improving the performances of energy-storage devices.