In this study, pyromellitic dianhydride (PMDA) modified waste sugarcane bagasse (SCB) was prepared through a simple method to remove two cationic dyes: methylene blue (MB) and malachite green (MG) from aqueous solution. Adsorption performances of MB and MG on the modified sorbent were investigated in details. The adsorption capacities of the modified SCB for MB and MG were 571.4 and 377.4mgg-1, respectively, which were 10 and 12 times than that obtained on the unmodified SCB. Adsorption kinetics study showed equilibriums were obtained after adsorption for 13 hours for both dyes. The modified SCB could be used repeatedly after regeneration. FTIR results showed that carboxyl and hydroxyl groups on the modified SCB involved in adsorption process.