The structure of milled wood lignin(MWL), isolated via the Bjrkman procedure, was studied by means of 1H NMR spectroscopy and Fourier transform infrared spectroscopy, and then its pyrolytic product distribution was investigated on a pyrolysis device. MWL obtained from Manchurian Ash(MA) contained more methoxyl and free phenolic hydroxyl groups per C9 unit than MWL from Mongolian Pine(MP) due to the existence of both guaiacyl and syringyl units, which have a major influence on the pyrolysis behavior of lignin. The results of pyrolysis show that MWL from MA generated a higher yield of bio-oil, mainly composed of phenols, guaiacols, syringols and catechols, and a less yield of char, in addition to the gaseous products CO, CO2, methane and methanol, compared with MWL from MP. Guaiacol and syringol were the typical products from G-lignin and S-lignin, probably attributed to the easier cleavage of the aryl-alkyl linkage in the side chain compared with the C―OCH3 bond in the benzene ring. The degradation of MWL from MP was dominated by the demethylation reaction and the cleavage of aliphatic ―CH2OH at the γ-position, followed by the cracking of the Cα―Cβ and C4―Cα bonds. The structure of milled wood lignin (MWL), isolated via the Björkman procedure, was studied by means of 1H NMR spectroscopy and Fourier transform infrared spectroscopy, and then its pyrolytic product distribution was investigated on a pyrolysis device. MWL obtained from Manchurian Ash (MA) contained more methoxyl and free phenolic hydroxyl groups per C9 unit than MWL from Mongolian Pine (MP) due to the existence of both guaiacyl and syringyl units, which have a major influence on the pyrolysis behavior of lignin. The results of pyrolysis show that MWL from MA generated higher yield of bio-oil, mainly composed of phenols, guaiacols, syringols and catechols, and a less yield of char, in addition to the gaseous products CO, CO2, methane and methanol, compared with MWL from MP . Guaiacol and syringol were the typical products from G-lignin and S-lignin, probably attributed to the easier cleavage of the aryl-alkyl linkage in the side chain compared with the C-OCH3 bond in the benzene ring . The degradation of MWL from MP was dominated by the demethylation reaction and the cleavage of aliphatic -CH2OH at the γ-position, followed by the cracking of the Cα-Cβ and C4-Cα bonds.