The pyrolysis of softwood (SW) kraft lignin in the presence of NiCl2 and ZSM-5 zeolite as an additive was examined at 700 degrees C. Gel permeation chromatography (GPC), quantitative C-13 and P-31 NMR were used to characterize the pyrolysis oil. Based on the results of C-13 and P-31 NMR for the pyrolysis oils, the use of zeolite during pyrolysis caused the near complete loss of aliphatic hydroxyl and carboxyl groups in the bio-oil and about 80% of methoxyl groups were also eliminated. The zeolite was shown to improve the decomposition of aliphatic hydroxyl groups, carboxyl, methoxyl groups, and ether bonds in the lignin during pyrolysis. In addition, as determined by C-13 NMR, the oxygen content in the bio-oil decreased after the use of zeolite. The results of GPC analysis indicated that the addition of H-ZSM-5 zeolite with lignin provided a bio-oil that had similar to 10% lower average molecular weight than the pyrolysis product acquired without the additive.