Due to the gravity of arsenic contamination and its potentially detrimental effects on public health, extensive endeavors have been undertaken to treat water sources harboring these hazardous pollutants. This study focuses on investigating the kinetics and equilibrium of biosorption of arsenic (III) and As(V) from aqueous solutions using mangrove leaf biomass (Avicennia marina). Optimal biosorption conditions were determined by considering the optimum pH, initial concentration of adsorbate, contact time, and adsorbent dose. Adsorption models like Langmuir's and Freundlich's were employed to describe the adsorption and determine the corresponding constants of the isotherm. The isothermal data for biosorption demonstrated acceptable compatibility for the Langmuir and Freundlich isothermal models. The maximum adsorption capacity of As(III) and As(IV) onto mangrove leaf biomass (Avicennia marina) was found to be 90.9 and 76.9 mg/g for As (III) and As (V), respectively. Moreover, the correlation between the kinetic experimental data and the second-order kinetic model was significant, indicating its suitability in describing adsorption.