Flexible polyaniline-carbon nanofiber (PANI-CNF) composites were fabricated and evaluated for use as supercapacitor electrodes. Sol-gel and electrospinning techniques were employed to produce flexible carbon nanofibers and polyaniline coating was applied via in-situ chemical polymerization to further improve the electrochemical properties of the electrodes. The performance of flexible PANI-CNF electrodes was investigated in symmetric supercapacitor cells. Results showed that binder-free flexible PANI-CNF electrodes had high capacitance of 234 F/g and excellent cycling stability with capacitance retention of about 90% after 1000 cycles. Ragone plots were also presented and a high energy density of 32 Wh/kg at the power density of 500 W/kg was achieved for the flexible PANI-CNF electrode prepared with 12 h polymerization. In addition, mechanical tests demonstrated that free-standing PANI-CNF electrodes were durable and highly flexible. Therefore, combining sol-gel and electrospinning techniques is a facile and effective way to achieve flexible carbon nanofiber electrodes and this work provides a new approach for designing flexible electrodes with exceptional electrochemical performance, which is very promising for practical application in the energy storage field.