Abstract: As a clean sustainable substitute for fossil fuel, bio-oil has properties of acidity and instability, which affected its large scale application. Based on its high acid, ketone, aldehyde and phenol content, three processes for the bio oil upgrading were investigated: Separated esterification and hydrogenation (SHE), one step esterification-hydrogenation (OEH), and one step esterification-hydrogenation plus second hydrogenation process (OEH plus). The studies were conducted over Mo modified Raney Ni catalyst (Mo-RN) and Ru/C catalyst with the light fraction of sawdust fast pyrolysis oil as feedstock. The catalysts reuse performance and the reaction pathways of the typical components during the bio-oil upgrading process were also studied. For the SEH process, esterification reaction was conducted without catalysts, and the hydrogenation reaction of the produced esterification bio-oil were carried out over Mo-RN and Ru/C respectively. For the OEH process, methanol and the raw bio-oil were reacted over Mo-RN and Ru/C directly. Based on OEH-Ni, second hydrogenation over Ru/C catalyst under mild condition (120℃) was conducted after the OEH-Ni process. Over all, the oil properties were improved significantly through the different upgrading process. Through the separate esterification process, oil acidity decreased substantially, showing the acid content decreased from 39.41% of the raw oil to 12.40% of the ES-oil. Accordingly, the total acid value decreased from 55.76 to 16.11 mg/g. In the following hydrogenation process, esters converted to corresponding alcohols under H2 atmosphere over Mo-RN and Ru/C catalyst, resulted in an alcohol content of 56.61% and 43.06%, respectively. Mo-RN showed better catalytic performance on the hydrogenation of phenol and ketone compounds. In the one step hydrogenation reaction process, Ru/C showed better performance for acid and ester converting to corresponding alcohols, showing the acid and ester content of 8.12% and 8.01% for OEH-Ru and 11.43% and 17.15% for OEH-Ni process. Mo-RN better improved the ketone and phenol conversion, showing the content of 1.56% and 6.60%. Through the OEH process, saturated alcohol & ester content increased from 9.99% in the raw oil to 58.31% and 71.95% for Ru/C and Mo-RN, respectively. For the one step hydrogenation over Mo-RN catalyst along with its following second hydrogenation process, acid, phenol and ester in OEH-Ni oil got more thoroughly conversion to alcohol compounds, leading to obtaining an OEH plus upgraded oil of 84.20% saturated alcohol and ester content. Meanwhile, through the second hydrogenation, oil properties showed great improvement for the total acid value decreasing from 111.52 to 11.75 mg/g and pH value from 3.67 increased to 5.88. Besides, even in the second use of Mo-RN and Ru/C catalyst, no significant deactivation was observed. The saturated alcohol and ester content was still kept at 68.37% and 75.84% degree for the OEH -Ni* and OEH plus process, respectively. Through esterification hydrogenation process, oil properties showed great improvement in the acidity and stability. This esterification hydrogenation method is proved to be a promising routine for efficient upgrading bio-oil to oxygenated fuel.