This study aims to synthesize carbon nanofiber as supercapacitor electrodes from pineapple leaf fibers using two steps. The first step involved varying the raw materials termed (i) pineapple leaves, (ii) pineapple leaf fibers, and (iii) the combination of both. The best electrochemical properties in the first step were used as raw material for the second step with varied KOH concentrations at 0.5 M, 0.7 M, and 0.9 M. Furthermore, the optimum specific capacitance based on cyclic voltammetry method for both steps were 175 F g−1 and 191 F g−1, respectively. For the second step, the physical properties, including density, surface morphology, elemental content, N2 gas adsorption–desorption isotherm, and crystalline structure, were analyzed. The result showed the density of the pineapple leaf fiber activated carbon (PALF-AC) electrode steadily declined from 27.93 to 51.72% after carbonization-activation. The optimum specific surface area is as high as 945 m2 g−1 for the PALF-AC0.9 electrode. In addition, the nanofiber diameter on surface morphology based on scanning electron microscopic (SEM) analysis in the range of 35–185 nm. Therefore, a carbon nanofiber–based electrode from pineapple leaf fibers (PALF) shows promising capacitive properties and great potential for use on energy storage devices.