•TG-cl-PAA/Fe3O4 nanocomposite hydrogel was used as an adsorbent for removal of dyes.•MG, ThT, and RhB dyes were removed efficiently from a ternary system.•The Qm for MG, RhB and ThT were obtained as 642.9, 552.6, and 413.6 mgg−1, resepectively.•The adsorbrnt showed good re-useability after regeneration.•Adsorption kinetics were well-fitted with the pseudo-second-order model. Performance of a magnetic tragacanth gum-crosslinked-poly(acrylic acid) (TG-cl-PAA/Fe3O4) nanocomposite hydrogel in removal of malachite green (MG), thioflavin T (ThT), and rhodamine B (RhB) cationic dyes from single, binary, and ternary systemes were investigated through the batch method. The adsorption parameters, including adsorbent amount, initial concentrations of dyes, pH, and contact time were optimized for all systems. Langmuir and Freundlich models were used for equilibrium adsorption isotherm investigation, and it was found that the Langmuir model is more fitted than those of the Freundlich model, which proved the linearity of the adsorption process. Maximum adsorption capacities (Qm) of TG-cl-PAA/Fe3O4 were calculated for all systems. The Qm for MG, RhB, and ThT dyes in ternary system were obtained as 642.9, 552.6, and 413.6 mgg−1, resepectively. The removal of all dyes in single, binary as well as ternary systems were well-fitted with the pseudo-second-order model that confirm the rate-limiting step might be the chemical adsorption. The developed adsorbent was regenerated through desorption process and reused for several times. It was found that the removal efficiency of adsorbent approximately remains the same for the first three cycles, and after which decreased gradually. Magnetic tragacanth gum-cl-poly(acrylic acid) nanocomposite hydrogel was applied for removal of malachite green (MG), rhodamine B (RhB), and thiflavin T (ThT) cationic dyes in single, binary, and ternary systems. Display omitted