Bio-oil derived from the fast pyrolysis of biomass is a multicomponent mixture comprised of over 400 types of organics, which need to be separated for specific applications. Moisture contents and acids also have to be removed from the compounds for efficient energy consumption. In this study, unlike the conventional approaches of separating bio-oil after condensation, we developed a multicondenser system for separating bio-oil compounds in order to better utilize them in different applications. A biomass sample (cotton stalk) was pyrolyzed in a fluidized bed reactor operated at 400 and 600 degrees C. The pyrolysis vapors passed through four condensers arranged in sequence at 300 degrees C, 100 degrees C, 0 degrees C, and -20 degrees C, respectively. Each component on fractions was more efficiently separated based on their varied boiling points. Each fractional bio-oil (FBO) exhibits different chemical and physical properties. Over 90% of small molecular materials including acetic acid, ketones, aldehydes, and water, were gathered in the 0 degrees C condenser, and the organics of midboiling points (phenols) were collected in the 100 degrees C condenser. In addition to acetic acid, phenols, which are weak acids, can also contribute to acidity of bio-oil.