The hydric sources in Algeria were missing significantly, so the government policy goes toward preservation of the surface water from pollutants originated of industrial rejects. Among of these contaminants we find the dyes which can pollute water surface even at low concentrations. The present work is focused on the treatment of water contaminated by Rhodamine B dye, which is used in microbiology as histological fluorescent dye. To achieve this purpose, a bioadsorbent named Lichen which is a kind of fungi that it deposits on the trees, was used to remove rhodamine B (RB) from aqueous solution. This bioadsorbent was brought from national Park of Theniet El Had (in the region of Tessimssilit, Algeria). The characterisation results showed that this material had a specific surface area equal to 5.02 m²/g and the value of point of zero charge was around pH 7. The sorbent was tested for rhodamine B adsorption at different experimental conditions such as solution pH, contact time, initial concentration of RB and temperature. The maximum RB amount adsorbed was 15.80 mg/g registered for pH and temperature equal to 4 and 40 °C, respectively. The adsorption equilibrium was attended in 90 mins. The experimental data were fitted by Langmuir, Freundlich equations and the most adequate model was Freundlich. The kinetic adsorption of RB onto lichen sample follows the model of pseudo-second order. The thermodynamic study revealed that the process was physic in nature and endothermic where the disorder of RB molecules increased at the interface solution solid.