This study focused on removing methylene blue (MB) from aqueous solutions using microalga Scenedesmus regularis as a biosorbent. The biomass was characterized by Fourier transform infrared spectroscopy (FT-IR) and field emission scanning electron microscopy (FE-SEM). The difference in thermal properties of the biomass was investigated by thermogravimetric analysis (TGA). The adsorption capacity of S. regularis was tested with different environmental key parameters (pH, temperature, biosorbent dosage, dye concentration, and contact time) in batch system experiments. The maximum adsorption capacity was 341.34 mg/g at a pH of 6.8, a temperature of 25 °C, a dye concentration of 250 mg/L, and a biosorbent concentration of 5 mg. Approximately 92% of the dye was removed within two minutes, and the removal efficiency reached 99% within 15 minutes. MB adsorption equilibrium data fit well with the Langmuir (R2=0.994) and Dubinin-Radushkevich (R2=0.993) isotherm models. The kinetic model of adsorption followed pseudo-second-order kinetics. Thermodynamic parameters showed that the adsorption process was endothermic and physical, favorable, and spontaneous. The results showed that S. regularis is an eco-friendly biosorbent with efficient performance that may be used for MB removal without any modification.