Various organics with quite different oxygen-containing functional groups mixing together in bio-oil lead to the high instability of bio-oils. A liquid-liquid extraction method was developed to separate the bio-oil into different chemical groups by their polarities to stabilize bio-oils and improve the quality. The separated bio-oil had similar oxygen-containing functional groups in different phases. Biomass pyrolysis using Douglas fir pellet and characterization of the bio-oil chemical compounds were conducted, followed by bio-oil liquid-liquid extractions with several solvents (e.g., hexane, petroleum ether, and chloroform). In comparison to the raw bio-oil, the solvent phase had high concentrations (85%) of phenols and guaiacols, while no sugar and very low acid and alcohol contents were detected, which were left in the water phases.