The removal of reactive black 5 (RB5) from aqueous solutions by adsorption onto multi-walled carbon nanotube (MWCNT) was studied. The effects of some operating parameters such as solution pH, initial dye concentration, adsorbent dosage and adsorption capacity on the adsorption of RB5 were investigated. It was found that RB5 removal by adsorption onto MWCNT was best achieved at natural pH. The adsorption efficiency of RB5 by MWCNT decreased with increasing initial dye concentration, while the increase of adsorbent dosage resulted in an increase of decolorization efficiency. The maximum adsorption capacity was reached at 36.2 mg/g after 90 min. The results obtained from kinetic studies reflected that RB5 removal fitted well with the second order model. Also, the isotherm data correlate well with the Freundlich model. The findings indicated that MWCNT can be used as a suitable adsorbent for removing dyes from wastewaters.