Abstract Background: At present study, acid modified banana leaf ash was used as an adsorbent for the successful removal of Reactive Black 5 (RB5) dye from aqueous environments. Materials and methods: The effect of various operating parameters such as pH of solution, dye concentration, contact time, adsorbent dosage, and the temperature was investigated. Results: Maximum adsorption capacity of the banana leaf ash was 191.32 mg/gat pH 2, the initial concentration of 200 mg/l and 323° K when 95.66% of the dye was removed. The process followed pseudo-second-order kinetics. Furthermore, equilibrium data were better represented by Freundlich isotherm among Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich equilibrium isotherm models. The negative values of free energy change confirmed the feasibility of the process and the spontaneous nature of adsorption. Furthermore, from the magnitude of ΔH, the process was found to be endothermic physisorption. Conclusion: According to the results of this study, it was found that the acid modified banana leaf ash is not only a low-cost adsorbent, but also has high performance in the removal ofRB5from aqueous environments.