In this work, orange bagasse has been used as an alternative adsorbent for removal of reactive blue 5G dye from an aqueous solution. The influence of the dye solution pH, the biosorbent drying, the dye solution temperature and biosorbent grain size was studied in batch systems, in order to improve the biosorption kinetics and the experimental equilibrium conditions. Batch kinetic experiments were carried out with different dye concentrations at two temperatures. The biosorption kinetic data were well fitted by both pseudo-first and second order models. The equilibrium adsorption data were interpreted by applying widely the isotherm models and a set of six BET isotherm-added-to other ones and their adjustable parameters were determined by the PSO method. The isotherm models with s-shaped behavior, such as the Langmuir-BET combined isotherm, have described satisfactorily the equilibrium data, suggesting that the dye removal is based on an adsorption process of multi-layers onto the orange bagasse. (C) 2010 Elsevier B.V. All rights reserved.