To meet the demand for the development of high energy storage devices, appropriate designs of advanced carbon nanostructures (CNs) with metal oxides are highly preferred. Herein, the surfaces of two advanced carbon nanostructures (CNs), g-C3N4 and carbon nanofibers, were modified by the addition of carboxyl functional groups and then bound to TiO2 nanospheres (TNS). The surface functionalization of CNs is an efficient approach for improving the performance of carbon-based supercapacitors by solving the dispersion problems. Field emission scanning electron microscopy and transmission electron microscopy images demonstrated the sheet, fiber, and sphere morphologies of g-C3N4 , carbon, and TiO2, respectively. According to the results of Fourier transform infrared spectroscopy, the carboxyl functional groups with CNs were confirmed. In a three-electrode system, the supercapacitance of fictitious electrodes was evaluated with a 4 M KOH electrolyte. The surface-functionalized hybrid electrode showed a specific capacitance (817 F g(-1)) at a current density of 0.25 A g(-1) superior to those of the other fictitious electrodes. The electrode showed stability for up to 2000 cycles, with 89.2% capacitance retention. The superior electrochemical properties of CNs-TNS were attributed to the synergetic effects of g-C3N4-CNF/TiO(2 )composition and its excellent accessibility, conductivity, surface functionalization, and strong chemical interface. This study positively encourages the manufacture and design of carbon nanostructure based metal oxide nanostructures for high-performance supercapacitor applications.