Abstract: Biomass activated carbon was prepared from discarded durian shell and longan shell by KOH chemical activation method, and their adsorption capacity of methylene blue (MB) in water was also investigated. The surface area test (BET), Fourier infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to characterize the prepared biomass activated carbon, and the effects of activated carbon amount, initial concentration of MB solution, reaction time, temperature and pH on the adsorption of MB were studied. Results indicated that the maximum adsorption capacity of durian shell (longan shell) activated carbon was 363 mg/g under the optimum conditions (initial MB solution concentration of 200 mg/L, carbon amount of 30 mg, pH8.0, 120 min). The specific surface area of durian shell and longan shell activated carbon were 999.63 m²/g and 1377.95 m²/g, respectively, and their average pore sizes were 2.13 nm and 2.20 nm, respectively. In addition, the surface of durian shell and longan shell activated carbon had a large number of pores and a certain laminar structure. The existence of these pores provides rich adsorption sites for activated carbon adsorption, and compared with commercially available activated carbon, it has a more dense pore structure and has a stronger adsorption capacity for methylene blue.