In the present study, magnetic cellulose/graphene oxide composite (MCGO) was prepared as a novel adsorbent to dispose of dye wastewater. The morphology and chemical structure of the MCGO composite were characterized by the Fourier transform infrared spectrometer (FT-IR), X-ray diffraction (XRD), and scanning electronic microscope (SEM). The adsorption of methylene blue (MB) onto MCGO was studied in relation to initial concentration of MB, contact time, adsorbent dose, and pH value of solution. Adsorption kinetics and the equilibrium adsorption isotherm were fitted by a pseudo-second-order kinetic model and Langmuir isotherm, respectively. The thermodynamic parameters indicated that the adsorption was spontaneous, favorable, and exothermic in nature. Furthermore, MCGO was very stable and can easily be recycled. The adsorption efficiency of MCGO was still over 89% after recycling for five times.