Increasing the capacitance and rate performance of the carbon-based electrodes used in flexible supercapacitors remains a key challenge for commercial viability. To meet these requirements, free-standing Ti3C2Tx MXene/ carbon nanofiber (CNF) electrodes were prepared by electrospinning of polyacrylonitrile (PAN) and carbonization for application as flexible supercapacitor electrodes. The effects of Ti3C2Tx MXene size on fiber formation and electrochemical performance were investigated. Ti3C2Tx MXene/CNF electrodes exhibited a specific capacitance of 90 F/g at a fast scan rate of 300 mV/s, which is almost 2.3 times higher than that of a pure PANderived CNF (38 F/g at 300 mV/s), while showing similar capacitance values of around 120 F/g at the slow scan rate of 2 mV/s. Due to the high degree of mechanical flexibility of CNFs, MXene/CNF based flexible supercapacitors also demonstrate long-term cycling stability (98% retention after 10 K charge-discharge cycles), and outstanding flexibility in dynamic bend tests. These results suggest that the MXene/CNFs have great potential for applications in flexible and versatile electronic devices.