Adsorption processes have been investigated and successfully applied in the removal of dyes from textile plant wastewaters. Activated carbon is one of the most commonly used adsorbents, due to its excellent characteristics and relatively low cost. However, its dye removal efficiency depends on several parameters, notably the chemical nature of the carbon surface. To enhance the adsorption capacity, different methods have been proposed in the literature, chemical modification using acidic agents being one of the most commonly used. In this study, the performance of samples of activated carbon chemically modified with nitric and phosphoric acid in the adsorption of Basic Yellow 28 is evaluated. The physical and chemical structure of these adsorbents was investigated using electron microscopy, X-ray spectrometry, and infrared spectroscopy, revealing significant modifications depending on the agent used. Adsorption tests were conducted at three different temperatures and the adsorption kinetics and isotherms were evaluated. Comparing the experimental data and results obtained with models reported in the literature showed that in both cases the pseudo-second order kinetics model and the Freundlich isotherms provided the closest fits. The samples modified with nitric acid presented better overall performance, particularly due to pore collapse observed for the samples treated with phosphoric acid, which caused a significant reduction in the surface area and total pore volume. These results indicate that the chemically-modified activated carbon can be employed in the removal of basic dyes from textile effluents, allowing the reuse of the effluent.