2-(Trimethylsilyloxy)ethyl methacrylate (SMA)-derived mesoporous carbon nanofiber composite containing MnO2 (Si-Mn-CNF) is fabricated by electrospinning method and found to be a very promising candidate for supercapacitor electrodes. Si-Mn-CNF possesses a large surface area of 707 m(2) g(-1), high pore volume of 2.35 cm(3) g(-1), and high mesopore fraction of 65%. Herein, SMA is used as an activating agent to develop the mesoporous structure by the thermal decomposition of SMA without activation process. As a result, Si-Mn-CNF exhibits a high specific capacitance of 200 Fg(-1) at a discharge current density of 1 mAcm(-2) and energy density of 23.72 Whkg(-1) at a power density of 400 Wkg(-1). in 6 M KOH aqueous electrolyte, due to the pseudocapacitive character associated with the surface redox-type reactions of the MnO2 nanoparticles (NPs). Furthermore, the Si-Mn-CNF electrode retains a specific capacitance of over 85% of the initial value at a discharge current density of 20 mAcm(-2) compared with only 40% for Mn-CNF without using SMA, due to the rapid diffusion of electrolyte ions and the decrease of resistive characteristics through the developed mesoporous structures. Therefore, Si-MnCNF with high mesoporosity induced by SMA exhibits excellent electrochemical performance in terms of high specific capacitance and energy density, and excellent capacitance retention.