Abstract: A series of bagasse-based activated carbon samples with different ZnCl₂ impregnation ratios (1~6) were prepared with the zinc chloride activation method using bagasse as the raw material in order to remove methylene blue (MB) in water. X-ray diffraction (XRD), scanning electron microscope (SEM) and N₂ adsorption and desorption isotherms (BET) demonstrate that bagasse-based activated carbon samples have less ash, richer surface pores and larger specific surface areas and pore volumes than commercial activated carbon and the pore structure of the bagasse-based activated carbon samples are related to the ZnCl₂ impregnation ratios. ZnCl₂-4-500-1 with ZnCl₂ impregnation ratio of 4 has the highest mesoporous rate (75%) among all the samples, which suggests that proper impregnation ratio is beneficial to the formation of mesopores in bagasse-based activated carbon samples. In addition, ZnCl₂-4-500-1 has the most excellent MB adsorption efficiency, exhibiting nearly 100% MB adsorption in a wide temperature range (25~65 ℃) and pH range (1~9) among all the samples. The pore size distribution results indicates that ZnCl₂-4-500-1 has abundant pores with about 1.36 nm diameter, which is in favor of MB molecular adsorption according to the adsorption theory. The XPS analysis reveals that ZnCl₂-4-500-1 has the highest nitrogen content and -OH and C＝O functional group contents, which are also the important factors for its excellent MB removal performance. The adsorption isotherm experiment shows that the adsorption of MB in water on ZnCl₂-4-500-1 conforms to the Langmuir isotherm adsorption model with a maximum MB adsorption capacity of 1 428.6 mg/g at 25 ℃. ZnCl₂-4-500-1 can sustain more than 80% MB adsorption efficiency even after 5 adsorption-desorption cycles. It also shows excellent adsorption performance for aniline blue and cationic red-46(X-GRL), which suggests that it is a high-potential bio-based activated carbon material in the decolorization of dye wastewater.