Abstract: The dissolved and colloidal lignin (DCL) under different autohydrolysis levels were isolated and purified from the poplar woodchips autohydrolysis liquor, and their structural features were characterized by series of instrumental analysis, i.e. Fourier transform infrared (FT-IR), 1H,quantitative 13C, 2D HSQC, and 31P nuclear magnetic resonance (NMR) spectroscopies, and gel permeation chromatography/multi-angle laser light scattering (GPC-MALLS). The condensation of DCL in the poplar autohydrolysis liquor remarkably increased with increasing autohydrolysis temperature (Tmax>170℃). Comparing with functional groups of the lignin in the autohydrolyzed poplar woodchips, the DCL had less aliphatic-OH groups, containing more condensed phenolic-OH and more non-condensed phenolic-OH groups, and appearing with higher syringyl OH/guaiacyl OH ratios. These results indicated that DCL underwent more sufficient dehydration of side-chain aliphatic-OH, hydrolysis reaction of β-O-4 linkages, and condensation reaction between each lignin units.