This investigation deals with the potential use of new activated carbon as an adsorbent. This later was prepared from wormwood residues consisting of Artemisia vulgaris pharmaceutic plant by-product. This carbon was characterized using a Scanning Electron Microscopy(SEM) and Fourier Transform InfraRed (FT-IR) techniques before and after treatment with phosphoric acid. Batch adsorption experiments were conducted to study the adsorbent effectiveness in removing a cationic dye, basic yellow 28, from an aqueous solution. The effects of adsorbent dosage, dye concentration, and initial pH on the elimination of the dye were analyzed. The results show that the equilibrium data were correctly represented using the Langmuir adsorption isotherm. The adsorption capacity of activated carbon toward the cationic dye was 357.14 mg/g obtained at 20°C. The kinetic study indicates that the adsorption process of dye on activated carbon follows a pseudo-second-order equation. The efficiency of this process was tested for real effluent; the adsorbent was able to reduce the concentration of total organic carbon.