In this research, a chitosan-immobilized magnesium oxide nanoparticle (CS-MgONP) was synthesized to evaluate it as a prospective adsorbent for a cationic Methylene Blue (MB) dye. For the synthesized adsorbent, functional groups were analyzed through Fourier transform InfraRed (FT-IR) spectroscopy. X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) were used to identify the structural and morphological observations. The evaluation of process parameters such as pH (5-9), CS-MgONP dosage (0.2-0.6g/L), initial MB concentration (10-30mg/L), and temperature (283-323K) on MB adsorption was done at an equilibrium agitation time of 70 min using Central Composite Design (CCD) of Response Surface Methodology (RSM). MB removal percentage of 94.51% (desirability=0.829) was obtained under the optimal conditions of pH=7.28, dosage=0.47g/L, initial MB concentration= 19.37mg/L and temperature =309.76K. The adsorption onto CS-MgONP fits well with pseudo-second-order kinetics equation and equilibrium data made the best fit with Langmuir isotherm with maximum MB uptake capacity of 163.87mg/g. © 2020, Iranian Institute of Research and Development in Chemical Industries. All rights reserved.