Biomass pyrolysis oil is a complex mixture containing a wide variety of oxygenated compounds, which results in difficulties in bio-oil upgrading. To gain a clearer understanding of the reaction pathways, seven compounds were chosen to represent biomass pyrolysis oil. In this paper, catalytic desertification was applied to convert the carboxylic acids into esters. The influences of reaction time and water content were studied, and a conversion rate about 80% of carboxylic acids was reached.