Chlorine-functionalized reduced graphene oxide was prepared by using graphene oxide and sulfuryl chloride as raw materials. It is firstly reported that the hydroxyl group in graphene oxide can be substituted by chlorine in sulfuryl chloride. The product has a wider pore size and average interlayer space, and its surface area can be easily utilized. The adsorption data indicate that the material has high adsorption capacity on methylene blue. The adsorption process follows a second-order rate and Bangham diffusion kinetic model. The adsorption of methylene blue preferably fitting the Langmuir adsorption isotherm suggests monolayer coverage of the adsorbed molecules. The adsorption capacity of the product for methylene blue is 221.4 mg g⁻¹ at room temperature, which is significantly higher than those of reduced graphene oxide (80.0 mg g⁻¹) and active carbon (46.7 mg g⁻¹).