Fly ash, which is a waste generated in local thermal power plants, has been collected and converted to a low-cost and efficient adsorbent. The prepared adsorbent has been characterized and used for the removal of a typical alkyl dinitro phenol compound, 2-sec-butyl-4,6-dinitrophenol (DNBP), from aqueous solution. Adsorption studies include the effect of contact time, temperature, initial solute concentration, adsorbent dosage, pH, and particle size on the uptake of DNBP. The results show that the high adsorption capacity and sufficient removal efficiencies can be achieved at an optimum pH of 4.0, using 5 g/L of adsorbent with a particle size of 160-200 mesh in 120 min of equilibration time. The adsorption of DNBP increased as the temperature increased, which indicated that the process was endothermic in nature. The thermodynamic parameters (such as the free energy, enthalpy, and entropy of adsorption) were calculated based on a statistical model. Interpretation of the results was given. Kinetic studies have been performed to understand the mechanism of adsorption. The adsorption occurred via a film diffusion mechanism at lower concentrations (<= 8.33 x 10(-5) M) and via particle diffusion at higher concentrations (>= 1.25 x 10(-4) M). The adsorption of DNBP followed pseudo-second-order rate kinetics. Some experiments have also been performed for the purpose of regenerating the used saturated fly ash. The results indicate that fly ash can be used for the efficient removal of DNBP from aqueous solutions.