In this study, adsorptions of heavy metal ions Co(II) and Hg(II) onto modified lignin from Ailanthus altissima woods by alkali glycerol delignification are presented. The Langmuir isotherm model is only applicable to batch adsorber systems where sufficient time is provided to allow equilibrium between toxic metal ion in solution and the toxic metal ion adsorbed on the media to occur. The maximum adsorption capacities are 7.1 - 7.7 and 4.4 - 5.3 mg per g of the modified lignin for), Co( II) and Hg( II), respectively. The adsorption of the heavy metal ions increases with pH.