In this study, the decolorization capability of various synthetic dyes using the chemically treated orange peel (CTOP) is highly effective. An uncomplicated consecutive chemical treatment process by sodium hydroxide and iso-propanol promotes enhanced adsorption capacity of the raw orange peel for cationic dyes and enables high removal efficiencies in a wide range of pH conditions. The highest removal efficiency of the CTOP for the dyes in the pH range of 3-9 follows the order, safranin (99 %, pH 3) > methylene blue (97 %, pH 5) > methyl violet (91 %, pH 9) > rhodamine B (37 %, pH 3) > Congo red (20 %, pH 5). The adsorption capacity of CTOP for methylene blue calculated from the Langmuir model ( ?? 2 > 0.99) is remarkably high at 294 mg/g, which is almost 1.5 times higher than that of the untreated orange peels. These results demonstrate the great potential of low-cost, effective CTOP for application in the purification of dye-contaminated water. The selective removal of certain groups of toxicants from contaminated water using bio-peels can be achieved via tailoring their surface properties as removing essential oils on surface peels to increase the pore, appearing dendrimer-like microspores.