A raw bio-oil (RBO) from pyrolysis of rice husk was upgraded by catalytic esterification with methanol over an acidic resin. Both RBO and the upgraded bio-oil (UBO) were analyzed with a Fourier transform infrared spectrometer, pH meter, and an elemental analyzer. They were extracted sequentially with n-hexane, CCl4, CS2, benzene, and CH2Cl2. All of the extracts were analyzed with gas chromatography/mass spectrometer. The results showed that the carboxylic acids (CA) in the RBO were converted to their corresponding methyl esters (MEs), leading to a significant increase in pH value from 2.8 (RBO) to 5.3 (UBO). The total extract yield of UBO is much higher than that of RBO. In total, 20 CAs and 19 MEs were identified. The CAs include two alkenoic acids, a cycloalkanecarboxylic acid, a hydroxyalkanoic acid, a hydroxyalkenoic acid, an oxyalkanoic acid, a methoxyoxyalkanoic acid, an alkanedioic acid, an oxyalkanedioic acid, an aminoalkanoic acid, two furoic acids, three substituted benzoic acids, and five substituted phenylalkanoic acids.