Activated carbon sourced biomass materials widely applied as the energy storage supercapacitors possess high porosity, large specific surface area, controllable surface morphology as well as low-cost. In addition, chemical activation agents are very significant in the process, which are adopted in the opening of active sites and pore structures of activated carbon. This study is aimed at combining a single-step activating process with the carbonization and activation, using KOH, NaOH, and ZnCl2 as agents in the preparation of carbon from low-cost reeds wastes. Furthermore, the resulting thermal stability, density of the electrodes, surface of morphology, microstructure, specific surface area and pore size distribution were investigated. The results show variation in surface area, where the largest was observed in KOH-activated carbon electrode at 1183.540 m² g-1, alongside high fibers density and low crystallinity properties. This was followed by the treatment with ZnCl2 and NaOH, showing 768.301 m² g-1 and 284.823 m² g-1, respectively. Subsequently, the symmetric supercapacitor cells produced with KOH-activated carbon electrode exhibited a high specific capacitance of 141 F g-1, and maximum energy density of 4.89 Wh kg-1, at the power density of 35.32 W kg-1