Red mud, a waste of the aluminum plant, is the result of calcination of bauxite ore with sodium hydroxide at high temperature and concentration. This waste, which is the fearful dream of alumina production factories, attracts attention with its rich iron content. In this study, magnetic activated carbon (MAC) was obtained from the co-pyrolysis of sugar beet pulp and red sludge. The removal of basic yellow basic yellow 5 GL (BY5GL) dyestuff from aqueous solutions was investigated with the obtained MAC. MAC was characterized by X-ray diffraction, F-TIR, SEM-EDX, DSC, VSM and BET surface area. VSM analysis revealed a magnetism of 46.11 emu/g. RSM Taguchi statistical analysis was utilized. According to the L16 orthogonal array consisting of 4 factors and 4 levels, the optimum MAC was obtained at 800 °C, 120 min, 5 impregnation and 0.5 biomass/K2CO3 ratio. Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherm equations were applied. Pseudo-first, pseudo-second and intra-particle diffusion kinetic models were analyzed. Langmuir adsorption isotherm and pseudo-second kinetic model gave the best results. It was observed that pH was the most effective parameter for BY5GL adsorption. The maximum adsorption capacity was found to be 175.4 mg.g-1 at pH 7, 20 °C, 360 min contact time, 5 g.L-1 adsorbent dosage and 50 mg.L-1 dyestuff concentration. Activation energy and thermodynamic parameters of the adsorbent were also investigated for dyestuff adsorption.