AbstractCatalytic fast pyrolysis of Alcell lignin with various additive ratios (5%, 10%, and 15%, mass ratio) of nano-NiO was investigated using a horizontal pyrolyzer. Characterization methods, including Fourier transform infrared spectroscopy (FTIR), gas chromatography (GC), gas chromatography coupled with mass spectrometry (GC/MS), and elemental analysis, were utilized to identify the catalytic fast pyrolysis products. The results indicated that the nano-NiO catalyst had remarkable effects on the yield and quality of these products. The formation of gases, especially CO, CO2, and CH4, were greatly promoted when the additive ratio increased, while the formation of bio-char was clearly inhibited. However, when the additive ratio was 10%, the maximum yield of bio-oil (53.09 wt.%) was obtained, and the corresponding maximum higher heating value (HHV) was 25.33 MJ/kg. Furthermore, nano-NiO caused a large variation in the species of the compounds in bio-oil. Operating with the optimal nano-NiO additive ratio (10%), the carbon conversion rate was 65.50%, and the energy conversion rate was 74.53%.