The biosorption of As(III) and As(V) from aqueous solution on lichen (Xanthoria parietina) biomass were investigated using different experimental parameters such as solution pH, biomass concentration, contact time, and temperature. The equilibrium data were evaluated by Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) isotherm models. The biosorption capacity of X. parietina for As(III) and As(V) was found to be 63.8mg/g and 60.3mg/g. The mean sorption energy values calculated from D-R model indicated that the biosorption of As(III) and As(V) onto X. parietina biomass took place by chemical ion-exchange. The thermodynamic parameters showed that the biosorption of As(III) and As(V) ions onto X. parietina biomass was feasible, spontaneous, and exothermic in nature. Kinetic examination of the sorption data revealed that the biosorption processes of both As(III) and As(V) followed well the pseudo-second-order kinetics. The arsenic ions were desorbed from X. parietina using both 1M HCl and 1M HNO3. The recovery yield of arsenic ions was found to be 80-90% and the biosorbent had good reusability after consecutive seven sorption-desorption cycles.