Heavy metal ions in wastewater have negative effects on humans and the environment. In this paper, the adsorption of lead and copper ions by modified eucalyptus lignin nanosphere (ECLNPs) was studied. The spherical alkali-lignin particles had a diameter of 50 nm, abundant carboxyl groups of 0.66 mmol/g, and relatively high adsorption performance. The equilibrium adsorption capacities of Pb(II) and Cu(II) by ECLNPs were 126.0 mg/g and 54.4 mg/g, respectively. Both Pb(II) and Cu(II) adsorptive processes fitted a pseudo-second-order kinetics model. In the simultaneous adsorption process of Pb(II) and Cu(II), ECLNPs had higher adsorptive selectivity for Pb(II) than Cu(II), and there was a competitive adsorption process between Pb(II) and Cu(II). This resulted from the lower hydration heat of Pb(II) in water, which leads to easier separation from water ligands. ECLNPs also showed good recyclability, with 16.6% and 21.1% loss in Pb(II) and Cu(II) adsorption capacity, respectively, after three consecutive adsorption-desorption cycles, which provides a feasible technical direction for the utilization of biomass resources and the treatment of water contamination.