The vapor-phase reactions of nascent volatiles derived from the, fast pyrolysis of lignin were investigated both experimentally and numerically. Lignin residue after enzymatic hydrolysis was pyrolyzed. in a two-stage tubular reactor at 773-1223 K. The nascent volatiles formed in the first stage underwent vapor-phase reactions in situ in the second stage. A detailed chemical kinetic model that consists of more than 500 species and 8000 elementary reactions was used to simulate the vapor-phase-reactions of volatiles derived from fast pyrolysis of lignin. The contribution of tar in the vapor phase reactions was considered in global reactions, which improves the predictive capability of the kinetic model. The experimental data and numerical predictions of 31 products were compared and analyzed to understand the mechanism of vapor-phase reactions of lignin. The model predictions were in good agreement with the experimental observations. Reaction pathway analysis for the formation of aromatic hydrocarbons was performed. Cyclopentadienyl radicals produced from phenol decomposition were suggested as important intermediates in the formation of aromatic hydrocarbons during lignin pyrolysis.