Water pollution by chemicals of industrial origin is one of the most serious problems affecting human health and the environment. Dyes produced by factories are considered to be one of the sources of pollution; they are organic, solid or liquid chemicals that can modify the physical, chemical or biological properties of water. The objective of this research was to remove water contaminated with a cationic dye using the batch adsorption method onto a local Algerian plant as the adsorbent. The plant was prepared, and the adsorption isotherms were studied under its operating conditions. The adsorbent selected for this work is common reed from southern Algeria, focused on the adsorption of methylene blue. Adsorption isotherm is a very important step in understanding adsorption mechanisms, and in determining the capacity and mode of adsorption in monolayers or multilayers. This step can be taken from equilibrium models describing the adsorption process. The experimental results in this study were obtained by applying the Langmuir and Freundlich models. The study of adsorption isotherms showed that the correlation coefficient R2 for the Langmuir model is higher than that obtained by the Freundlich model R2 is equal to 0.9936; 0.974; 0.999 and 0.9872 which is higher than 0.9234; 0.9533; 0.9669 and 0.9432 at temperatures 298, 308, 318 and 328 K, respectively. From this comparison of results, it can be deduced that the Langmuir model is more suitable for modeling methylene blue adsorption with a maximum adsorption capacity equal to 31.4465 mg/g at 328 K. Methylene blue adsorption was monolayer. Finally, the results obtained indicate that the adsorption of methylene blue on common reed is favorable, enabling us to assert that this adsorbent can be used in such purification operations with interesting efficiency, which can be a good indicator and motivation for future studies and experiments.