Mesopore-enriched activated carbon nanofiber (ACNF) mats are produced by incorporating vanadium(V) oxide (V2O5) into polyacrylonitrile (PAN) via electrospinning, and their electrochemical properties are investigated as an electrode in supercapacitors. The microstructures of the ACNFs (e.g., nanometer-size diameter, high specific surface area, narrow pore size distribution, and tunable porosity) are changed, and the textural parameters are found to affect the electrochemical properties significantly through the different V2O5 loadings and activation process. The V2O5/PAN-based ACNF electrodes with well-balanced micro/mesoporosity having an optimal pore range for effective double layer formation in an organic medium are expected to be useful electrode materials for supercapacitor applications.