In this research, multi-walled carbon nanotubes-CoFe2 O4 magnetic (MWCNTs-CoFe2 O4 ) based-magnetic nanocomposite was used for removal of Remazol Brilliant Blue Reactive (RBBR) dye, which is one of the most widely used organic dyes in the textile industry. The various characterization methods such as Fourier-transform infrared spectroscopy, field-emission scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, transmission electron microscopy, Brunauer–Emmett–Teller and vibrating sample magnetometer were used to confirm the formation of nanocomposite adsorbent and study its magnetic properties. The effective parameters on the removal process were time, adsorbent dose, dye concentration, pH and temperature. The optimal values of each of these parameters were determined as 40 min, 0.4 g, 20 mg/L, 3 and 298 K, respectively. The removal efficiency of RBBR dye in the presence of MWCNTs-CoFe2 O4 nanocomposite was 95% under optimal conditions. The maximum adsorption capacity (qmax) of MWCNTs-CoFe2 O4 for RBBR dye was 106.5 mg/g. The obtained experimental data were then analyzed with different isotherms such as Langmuir, Freundlich and Temkin and the results showed a very good agreement of the data with the Langmuir isotherm (R² = 0.9998). In addition, two quasi-first-order and quasi-second-order kinetic models studied the kinetic of the adsorption process. It was observed that the process follows the quasi-second-order kinetic. Finally, a thermodynamic study was carried out at four temperatures of 298, 308, 318 and 328 K to calculate the Gibbs free energy (ΔG) changes, enthalpy changes (ΔH) as well as entropy changes (ΔS). The calculated values for the mentioned thermodynamic parameters were –8.93 kJ/mol, –32.38 kJ/mol and 0.078 kJ/mol K, respectively. The results showed that dye adsorption is an exothermic, spontaneous process and is associated to a reduction in system irregularities. [ABSTRACT FROM AUTHOR]