Poly-α,β-DL-aspartic acid is known as a green chelant of various metal ions. To provide a novel nanochelant for treating Pb(II) poisoning, poly-α,β-DL-aspartic acid was modified with L-Cys to form poly-α,β-DL-aspartyl-L-cysteine (PDC; MW, 27273). DL-Asp was converted into polysuccinimide through a thermal polycondensation, and the amidation of polysuccinimide with L-Cys provided PDC. In water, PDC formed various porous nanospecies. In the mouse lead intoxication model, both intraperitoneal and oral administration of PDC (0.1, 1.0, and 10.0 nmol/kg) dose dependently removed Pb(II) accumulated in the organ, bone, and blood. PDC did not remove the essential metals including Cu(2+), Fe(2+), Mn(2+), Zn(2+), and Ca(2+) of the treated mice. The porous feature and size of the pH- and concentration-dependent nanospecies of PDC benefited the removal of Pb(II).