In this paper, the porous manganese dioxide (MnO2) was prepared by an interfacial reaction of potassium permanganate in water/ferrocene in chloroform. The surface area and pore distribution of MnO2 can be controlled by simply adjusting the reaction time and the content of surfactant in the aqueous phase. The electrochemical performance of the prepared MnO2 was evaluated as an electrode material for supercapacitors by the means of cyclic voltammetry and galvanostatic charge–discharge tests. Electrochemical tests results indicated that the pore size plays an important role at high charge–discharge rate, the sample with a large pore size shows a better rate capability, while the sample with a small pore size but large surface area delivers a large capacitance at low current rate.