The carboxylic acids in fast pyrolysis oil (bio-oil) are one of the detrimental properties that impede its straightforward application in internal combustion engines. In this paper, a novel approach is proposed to convert the carboxylic acids in bio-oil to ketones efficiently. That is, the acids in a bio-oil derived from pyrolysis of rice husk were firstly transformed to their calcium salts by neutralization with CaCO3 and then subjected to decarboxylation at high temperature to form ketones and regenerate CaCO3 simultaneously. Due to various carboxylic acids contained in the bio-oil, both symmetric and asymmetric ketones were formed. Although phenols, aldehydes and saccharides had almost unnoticeable effect on the decarboxylation of carboxylic acids, they, particularly saccharides, tended to undertake carbonization reaction, leading to the char formation associated with CaCO3 regenerated. After decarboxylation, the acidity of the upgraded bio-oil decreased dramatically from 167.62 to 1.98 mg of KOH/g, whereas its HHV increased from 18.38 to 27.59 WIT. Although the upgraded bio-oil yield was only 46.10%, the energy efficiency could be reached to 69.20%. Decarboxylation of the water-soluble fraction, which was obtained by water extraction of the bio-oil, was also investigated. With the aid of water extraction, most of the acids and saccharides could be enriched in the water-soluble fraction, while the phenols were concentrated into the oil-soluble fraction. After decarboxylation of the water-soluble fraction, the HHV and acidity of the upgraded bio-oil were improved to be 30.05 MJ/kg and 1.03 mg of KOH/g, respectively. The energy efficiency could be enhanced to 77.59%. (C) 2017 Elsevier Ltd. All rights reserved.