In this study, carbonaceous material was prepared from waste cotton (CT1000). Yield, base consumption, pH, specific surface area, pore volume, and mean pore diameter of CT1000 were investigated. Specific surface area and pore volume of CT1000 was greater than that of CT (virgin waste cotton). Kayacryl Yellow (KY: yellow dye) was used for adsorbate. The equilibrium adsorption was reached within 48 h. The adsorption rate data was fitted to the pseudo-second-order kinetic equation, which indicated that reaction rate was in proportion to the square of adsorbate concentration in aqueous solution systems. Moreover, the adsorption isotherm data was fitted to the Freundlich equation. Amount of KY adsorbed onto CT1000 in the presence of dye assistant auxiliaries was similar trend to that onto CT1000 in the absence of dye assistant auxiliaries. These results showed that CT1000 was useful for purification of wastewater containing dyestuffs.