Bio-oil that is currently produced from lignocellulosic biomass requires significant modification to become an exceptable transportation fuel Due to its high acidity and chemical instability, many problems arise in handling and utilization. To facilitate the use of bio-oil as a feedstock for chemicals and fuels, there is considerable interest in upgrading bio-oils through chemical pathway;. We discuss our observations on ozone oxidation of bio-oil, and synthesis of upgraded bio-oil by subsequent esterification. It was found that the acid value of bio-oil was increased from 45.4 to 118.4 mg KOH/g after oxidation. To decrease the acid value, the oxidized bio-oil was further reacted with butanol to in-Trove fuel properties. Upgrading bio-oil in the conditioned experiment was investigated, in which water content of bio-oil was lowered markedly from 45% to 1-2%. In addition, density of the upgraded bio-oils was observed to decrease from 1.13 to 0.94 and 0.92 kg/m(3), and the gross calorific value increased by 163% and 177% by ozone oxidation and without oxidation, respectively.