A facile and green hydrothermal approach was employed to fabricate the magnetic carboxyl-functionalized attapulgite/carbon nanocomposites based on the spent bleaching earth. The preparation process simultaneously involved the growth of magnetic nanoparticles and the coating of carbon species with carboxyl groups on the surface of attapulgite via hydrothermal redox reactions between Fe(III) and sodium citrate in the aqueous solution. The composition, magnetic response as well as adsorption properties of as-prepared nanocomposites could be facilely controlled by adjusting the concentration of sodium citrate. The resultant adsorbents possessed fast adsorption kinetics and the maximum adsorption capacity toward MB and Pb(II) could reach 254.83 mg/g and 312.73 mg/g while the concentration of sodium citrate was 0.6 M. In addition, the adsorbent could be easily recycled due to its magnetism and the adsorption capacity had a slight decrease after six adsorption-desorption cycles. All the information revealed that the carboxyl-functionalized attapulgite/carbon nanocomposites were expected to be a promising candidate for high-efficient removal of contaminants from wastewater in future practical use.