Abstract: A storage stability test was conducted on the bio-oil produced by fast pyrolysis of pine and corncob. The viscosity, water content and solids content of bio-oil increased after storage. However, there were no significant changes in the pH value, heating value and density of bio-oil. The quantitative analysis by GC/MS showed that the content of 1-hydroxy-2-propanone, acetic acid, and furfural were significant decreased. The content of 2-methoxy phenol, 4-methyl-2-methoxy-phenol, and 4-methyl-phenol increased. ¹³C NMR spectral analysis showed that the alkyl carbon and di-O-alkyl carbon content of bio-oil decreased after storage, while the content of aromatic and unsaturated carbon increased. Therefore, the aromaticity of bio-oil increased.