Detailed structural features of lignin from hydroxycinnamoyl transferase (HCT) down-regulated poplar has not been thoroughly illustrated. In the present study, MWL and CEL samples were successively extracted with higher yield and purity. NMR spectra demonstrated that the MWL and CEL presented similar structural features (beta-O-4', beta-beta', beta-5', and beta-1', although the subsequent CEL had a high beta-O-4' linkages content and S/G ratios, which are also related to their molecular weights. There were no significant differences in S/G ratio and the distribution of the inter-unit linkages between the control and HCT down-regulated poplar (HCT poplar). However, a minor amount of H units were detected in lignin of the HCT poplar. In addition, p-hydroxybenzoate (PB) content was observably increased in the lignin from the HCT poplar. These findings are of very importance in assessing of the digestibility of HCT down-regulated poplar in the fuel production. (C) 2014 Elsevier Ltd. All rights reserved.