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This study examines the ability of Stipa tenacissima L. (Alfa) to biosorb the Methylene Blue dye. Biosorption tests were performed in aqueous solution based on certain essential parameters such as solution?s pH (2-12), solid/liquid ratio (1-6 g/L), initial dye concentration (25-125 mg/L) and contact time (0-300 min). The Langmuir, Freundlich, Temkin and Elovich models were applied. It was found that the equilibrium data could be fitted to the Langmuir isotherm for MB biosorption with a maximum capacity qmax 55, 95 mg/g. The kinetic study shows that the experimental data correspond to the pseudo-second order kinetic model. The negative Gibbs values free energy ?G? reveal the spontaneity of MB biosorption at the surface of Stipa tenacissima L. The positive value of ?H? reveals the endothermic nature of the process.