The nanocomposites Mg(OH)₂/graphene (nano-MG) were controllably prepared by a facile cathodic electrodeposition. The samples were characterized by field emission scanning electron microscopy with energy dispersive spectroscopy (FSEM-EDS), X-ray diffraction (XRD), Raman spectroscopy, thermogravimetric analysis (TGA), N₂ adsorption–desorption analysis and UV-vis spectrophotometry. Characterization results suggested that Mg(OH)₂ and graphene were combined successfully. Furthermore, the effects of the current density on the specific surface area of nano-MG have been investigated systematically. The specific surface area of nano-MG varied from 110 m² g⁻¹ to 525 m² g⁻¹, indicating that a suitable current density (0.07 A cm⁻²) is favorable for the uniform growth of Mg(OH)₂ on the surface of graphene. In addition, the nano-MG (0.425 wt% graphene) with a specific surface area of 525 m² g⁻¹ was used as an adsorbent to remove Methyl Orange (MO) from water. The results showed that the adsorption of MO onto nano-MG exhibited a maximum adsorption capacity of 1.074 g g⁻¹. Desorption experiments were carried out to explore the feasibility of adsorbent regeneration. And the possible mechanism responsible for electrodeposition and adsorption of MO on nano-MG were also elucidated.