Crofton weed (Eupatorium adenophorum Spreng) is an invasive species in China, which has damaged native ecosystems and caused great economic losses. To use the weed instead of simple control and management of it, the weed stem of was delignified by Acetosolv and Milox processes to obtain lignin. The lignins (Acetosolv lignin, AL; and Milox lignin, ML) were characterized and compared through several analysis methods. It was found that both of AL and ML were syringyl-guaiacyl type (GS) lignin, but that the chemical composition and structure of the two lignins were somewhat different. The obtained C-9 expanded formulas for AL and ML were C9H9.16O3.50N0.13(OCH3)(0.97)(Ph-OH)(0.34)Ac-0.22 and C9H7.9O3.13N0.13(OCH3)(1.23)(Ph-OH)(0.51)Ac-0.14, respectively. According to an elementary analysis, the two lignins had similar higher heat value of 20.0-21.0 MJ kg(-1), which were similar to that of raw coal. Gel permeation chromatography analysis indicated the two lignins had similar molecular weights. Notwithstanding that the Ultraviolet, Fourier transform infrared, and H-1-NMR spectra illustrated that the two lignins had similar chemical functional groups, the AL showed more acetyl groups signals. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 114: 1295-1302, 2009