In the present work lignin isolation from black liquor resulting from the Miscanthus sinensis pulping with 7.5% soda has been studied. M. sinensis is a raw straw widely studied as energy crop and for cellulose pulp production. Selective precipitation was achieved by decreasing black liquor pH from 12.64 to 0.72 and by adding sulphuric acid (98%, w/w). The precipitate percentage was obtained at each pH, regarding total dissolved solids. A considerable increase in the amount of precipitate was observed while lowering the pH as well as the attenuation in black liquor's colour. All samples along with commercial alkaline lignin were characterized by FT-IR, DSC, TGA, GPC and H-1 NMR to determinate the physico-chemical properties and structural features, and the results are reported. (C) 2009 Elsevier B.V. All rights reserved.