To determine the effect of crystal sizes of ZSM-5 and feedstock species on aromatic yield and selectivity from catalytic fast pyrolysis of biomass, catalytic fast pyrolysis (CFP) of different feedstock species (cellulose, hemicellulose, lignin, pine, corncob and straw) over ZSM-5 with varying crystal size (2 mu m, 200 nm and 50 nm) was conducted in a Pyroprobe pyrolyzer (5200, CDS Analytical). The experimental results show that ZSM-5 with crystal size of 200 nm exhibited the maximum aromatic yield and minimum BTX selectivity. The results could be attributed to its highest micropore surface area, amount of weak acid and maximum Bronsted to Lewis acid sites ratio (B/L ratio). Cellulose, hemicellulose and lignin play very different roles in catalytic fast pyrolysis of biomass. Cellulose exhibited the maximum aromatic yield of 38.4% and minimum non-condensable gas yield of 18.4%. Lignin showed the highest coke yield of 68.6% and lowest aromatic yield of 10.2%. And hemicellulose displayed the lowest coke yield of 29.4% and highest yield of non-condensable gas of 39.1%. (C) 2013 Elsevier B.V. All rights reserved.