The equilibrium and kinetics of the biosorption of Reactive Orange 13from aqueous solution were investigated using dead biomass of Rhizopus arrhizus in a batch system. Biosorption equilibrium was established in about 180min. The sorption data obtained at pH 2.0 conformed well to the Langmuir isotherm model. The biosorption data of Reactive Orange 13 were analyzed using the pseudo-first order, the pseudo-second order, Elovich kinetics models as well as intra-particular rate diffusion and liquid film diffusion models. The pseudo-second-order equation was the most appropriate equation to predict the biosorption kinetics. The reusability of the biosorbent was tested in five consecutive adsorption–desorption cycles and the regeneration efficiency was above 95%. The XRD, BET, SEM and FITR analyses helped to elucidate the mechanism of biosorption. From the practical viewpoint, the abundant and inexpensive dead fungal biomass could be used as an effective, low cost and eco-friendly biosorbent for the removal of Reactive Orange 13from the aqueous solution.