RuO2/carbon nanofiber composites fabricated by precipitating RuO2 on electron carbon nanofibers through the sol-gel process were tested as binder-free supercapacitor electrodes. We demonstrated that RuO2 dispersion and the resulting electrochemical performance of the composites could be tailored by surfactants. When sodium dodecyl sulfate was used, the composite composed of fine RuO2 nanoparticles attached to the fiber surface, and the amount of RuO2 increased considerably compared with that of the composite synthesized without adding any surfactant. After thermal treatment, RuO2 formed a wrinkle-like structure, and hydrous RuO2 partially converted to crystalline RuO2. Favorable specific capacitance of 546 F/g and RuO2 utilization of 80% at the scan rate of 2 mV/s were detected andwere attributable to the strong association between RuO2 and carbon nanofibers and the optimal content of hydrous RuO2 and crystalline RuO2 in which hydrous RuO2 provided pseudocapacitance, whereas crystalline RuO2 offered favorable electrical conductivity. By contrast, the use of cetyltrimethylammonium bromide (CTAB) to fabricate the composite resulted in poorly dispersed RuO2 particles, which weakly associated with carbon nanofibers. Additionally, CTAB promoted the development of crystalline RuO2, causing the loss of pseudocapacitance. Consequently, this composite exhibited low specific capacitance and apparent capacitance decay after 2000 cycles. (C) 2019 The Electrochemical Society.