Abstract Removal of a reactive dye, Reactive Black 5, from an aqueous solution was studied by adsorption on powdered activated carbon (PAC) and Afsin-Elbistan fly ash (Turkey). The adsorption of the dye on PAC and fly ash was investigated during a series of batch adsorption experiments carried out to determine the effect of initial dye concentration and contact time. The amounts adsorbed at equilibrium were measured. The Langmuir and Freundlich isotherm models were tested for their applicability. The equilibrium data satisfied both Langmuir and Freundlich models. The adsorption capacity of PAC and fly ash were found to be 58.823 mg and 7.936 mg dye per gram of adsorbent, respectively. The experimental data were analysed using the pseudo-first-order and pseudo-second-order adsorption kinetic models. According to these models, the rate constants were evaluated for initial dye concentrations. The experimental data fit the second-order kinetic model.