Adsorption is a simple and easily operated treatment process for water and wastewater reclamation. However, the cost of activated carbon (adsorbent) is an obstacle for this process to be widely employed in developing and underdeveloped countries. Hence, a low-cost and easily available Duckweeds plant has been used as the raw material for the synthesis of low-cost activated carbon. In this study, the effect of activating agents; potassium hydroxide (KOH) and phosphoric acid (H3PO4) on the properties of the activated carbon produced from Duckweeds plants was investigated. Duckweeds plants that were impregnated with an activating agent with a ratio 1:2 were carbonized in a tube furnace for two and a half hour at 550ºC with continuous nitrogen flow. After that, the synthesized activated carbon was used to remove methylene blue dye from aqueous solution. It was observed that activated carbon impregnated with H3PO4 possessed a more extensive exfoliated and multilayer structure, which gave rise to better adsorption performance compared to activated carbon impregnated with KOH. Furthermore, the porosity of the activated carbon impregnated with was much higher (38 ± 6%) compared to the sample impregnated with KOH (22 ± 4%). Indeed, the removal of dye for the former was slightly better (3-5%) and achieved equilibrium adsorption within a shorter duration. The findings show that H3PO4 is a better activating agent to induce exfoliated and multilayer structures on the activated carbon, where both of these characteristics are important for a good adsorption process. Overall, Duckweeds plants are a feasible source for the synthesis of low-cost activated carbon. Considering that Duckweeds plants can be used to remove nutrients presence in the wastewater, the activated carbon synthesized from the plants can be incorporated into the existing wastewater treatment plant as an additional purification process.