The physico-chemical characterization of two types of alkali lignin from different origin, namely L1 and L2, were studied by Fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance spectrometry (1H NMR) and gel permeation chromatography (GPC) analysis. FT-IR spectra show that they have the characteristics of absorption peaks of syringyl and guaiacyl. 1H NMR spectra indicate that acetylated L1 exhibits higher content of aromatic protons than L2, as the former is mainly composed by G units. L2 presents high quantities of methoxyl groups. GPC results show that L1 has much higher weight average than L2. They had similar functional groups, however, there were differences in the relative contents of functional groups.