In this article, buckthorn twigs were used to prepare activated carbon preparation by chemical activation with a microwave technique for removing diesel oil from water. buckthorn twigs and activated carbon were characterized by FESEM, EDX, and FTIR analysis techniques. Design-Expert (13 Stat-Ease) with Response Surface Methodology (RSM) was selected to identify and analyze the effects of activated carbon preparation factors. These factors include impregnation ratio, impregnation time, and microwave power with exposure time on the adsorption of methylene blue dye (MBN). Likewise, the effects of adsorption factors including; diesel oil concentration, pH, adsorption time, and adsorbent dosage on the removal efficiency were studied. The results showed that the maximum removal efficiency was 96.0823% with the significance of all adsorption factors. The adsorption data were fitted with the adsorption isotherm and kinetics models. The results showed that Freundlich and second-order kinetic models well described diesel oil adsorption, thus elucidating the applicability of multilayer and chemosorption processes. In addition, the thermodynamics parameters of diesel oil adsorption were determined, and the results demonstrated a spontaneous and endothermic adsorption process.