In this paper, the potential of two low-cost adsorbents such as sunflower seed shells (SS) and mandarin peelings (MP) in the removal of the synthetic anionic dye Reactive Black 5 (RB5) from aqueous solutions was investigated. SS led to a percentage of dye removal higher than MP (85% and 71% after 210 min, respectively, for an initial RB5 concentration of 50 mgL(-1) and an initial pH of 2.0). The rate of adsorption followed a pseudo-second-order kinetic model and the intra-particle diffusion was found to be the rate-controlling stage. In addition, the equilibrium data fitted well both the Freundlich and multilayer adsorption isotherm equations indicating the heterogeneity of the adsorbent surface. This was also corroborated by the SEM photographs. On the whole, the results in this study indicated that SS were very attractive materials for removing anionic dyes from dyed effluents. (C) 2007 Elsevier B.V. All rights reserved.