In this study, methylene blue (MB), orange II (ORII), and indigo carmine (IC) were used as adsorbates. Untreated (CT) and treated cotton (CT400, CT600, CT800, and CT1000) were prepared from waste cotton, and their respective physical (i.e., specific surface area, pore volume, and mean pore diameter) and chemical properties (i.e., yield percentage, base consumption, and amount of pH solution added to the adsorbent) were investigated. Scanning electron microscope images of CT, the adsorption rate, and the adsorption isotherm were also analyzed. The specific surface area, pore volume, and mean pore diameter of CT1000 was greater than that of other CT varieties, indicating that the pores on the CT surface were generated by carbonization. Additionally, yield percentage and base consumption decreased because of carbonization. Equilibrium adsorption (i.e., MB, ORII, and IC) was reached within 12 h. The experimental data were fitted to a pseudo-second-order model, suggesting that the adsorption might be a chemisorption process, for which the correlation coefficient, R, equals 1.000. The amount of dye adsorbed onto CT1000 was as follows: IC (290 mg/g) < MB (446 mg/g) ∼ ORII (452 mg/g). These experimental data were fitted to the Freundlich equation. The present study implies that the adsorbent for dye removal can be produced from waste cotton and that it is useful for the purification of dye solution systems.