In this study, the reduced graphene oxide was modified by grafting thymine on its surface. The resultant reduced graphene oxide-thymine composite (rGO-Thy) exhibits a higher Hg(II) adsorption capacity and selectivity compared with rGO as the functional group of thymine shows a strong affinity toward Hg(II) and forms the thymine-Hg(II)-thymine complex. The relative selectivity coefficients of rGO-Thy for Hg(II)/Pb(II), Hg (II)/Ni(II), Hg (II)/Co(II), Hg (II)/Cu(II), and Hg(II)/Cd(II) are 21.72, 7.08, 5.37, 4.37, and 10.51, respectively. This is mainly attributed to the thymine-specific binding with Hg(II). In addition, the adsorption capacity of rGO-Thy for Hg(II) is almost 2 times higher than reduced graphene oxide (rGO). Kinetics studies indicate that the adsorption process fits well with the pseudo-second-order model, and the adsorption kinetic constant is 0.02 g.mg-1.min-1. Moreover, the practical application of rGO-Thy achieves almost 100% removal efficiency, and the treatment volumes of actual industrial wastewater using a fixed bed column are as high as 390 BV for Hg(II), which indicates that rGO-Thy has great potential in advanced wastewater treatment.