Freestanding electrodes with high capacitive performances are designed and constructed for flexible solid-state supercapacitors. Self-supporting electrospun CNFs (carbon nanofibers) networks with high surface areas and good conductivities were used as both internal current collectors and supports for pseudocapacitive materials. Repetitive in situ chemical polymerization of aniline monomers was adopted to deposit PANI (polyaniline) nanoflakes on CNFs continuously, with the advantages of good uniformity and controllable mass loading of PANI on CNFs. The specific capacitances of the as synthesized series of CNFs/PANI composites based electrodes increased dramatically from 257 to 407 Fig accompanying with the increased mass loading of PANI from 32 to 78 wt.%. Moreover, two pieces of the obtained freestanding CNFs/PANI composite electrodes were also assembled into a solid-state supercapacitor by using polyvinyl alcohol/H2SO4 gel as electrolyte. The as-fabricated device presented excellent electrochemical performance with a specific capacitance of 201 F/g, an energy density of 4.5 Wh/kg at the power density of 103 W/kg, 80% capacitance retention after 6000 cycles, low leakage current and self-discharge characteristics and good flexibility. The flexible solid-state supercapacitors based on the freestanding CNFs/PANI composites might have potential applications in portable and flexible electronics. (C) 2015 Elsevier Ltd. All rights reserved.