In order to explore greater potential of carbon nanotubes(CNTs) in removal of hazardous chemicals in waste water, short multiwalled carbon nanotubes(MWCNTs) were chemically grafted by polyethylenimine (PEI) with a high density of amines in this study. The characteristics results of TG, Raman and XPS show that PEI was successfully grafted onto the surface of MWCNTs for the adsorption of a novel anionic dye methyl blue (MB) under laboratory conditions. The new MWCNTs-PEI adsorbent contributes to an enhancement of the adsorption capacity in MB removal. The maximum adsorption capacity for MB is estimated to be 418mg/g at 35 °C. The MWCNTs-PEI has a fast adsorption rate for MB in the first 5min and high adsorption capacity. The adsorption of MB onto CNTs-PEI is found to be dependent on pH, initial concentration and temperature. It’s found that equilibrium data for MB adsorption is fitted well by Langmuir isotherm model. The adsorption kinetics of MB is found to follow a pseudo-second-order kinetic model. The CNTs-PEI removal efficiency remains above 85% during the three cycles of the adsorption-desorption process. The MWCNTs-PEI could serve as a promising adsorbent for MB removal in wastewater.