Aiming to retard the self-polymerization of the reaction intermediates during bio-oil upgrading process, a large amount of alcohol (e.g., 50 wt% with respect to bio-oil) was used in the stabilization of fast pyrolysis oil by esterification before hydrotreatment by the authors in a previous work. In order to reduce the amount of alcohol use and hence improve the process economy, effects of stabilizing fast pyrolysis oil by esterification with methanol, ethanol or glycerol at a small loading (5 wt% w.r.t. bio-oil) in the presence of Amberlyst-35 DRY - A solid acid catalyst on the subsequent hydrotreatment of the oil were investigated. The bio-oil hydrotreatment experiments were carried out at 300 and 350 °C in a combined batch and semi-batch operation mode with Ru/C catalyst. The results demonstrated that, although stabilization of the pyrolysis oil by esterification with a small alcohol loading had least effects on the mass and carbon distribution in the hydrotreatment products and the elemental composition of the hydrotreated oil products, it could effectively reduce the molecular weight of the feed, prevent self-polymerization and decrease the overall molecular weight of the hydrotreated oil products.