Magnetic quaternary chitosan salt CS/EPTAC/Fe3O4 was used for the removal of acid red 1 (AR1), xylenol orange (XO) and alizarin red (AR) in single, binary and ternary systems. In the single system, the maximal adsorption capacity was 781.55 for AR1, 537.40 for XO and 992.61 mg g−1 for AR at pH 3.0 and 25 °C. The adsorption kinetics of the three dyes followed the pseudo-second-order model. In the multicomponent system, preferential adsorption was observed for AR at low adsorbent quantities due to the small size of the molecule. When the adsorbent amount was greater, AR1 was adsorbed first because of the greater number of sulfonic acid roots. In the entire adsorption process, XO always adsorbed most slowly.