Abstract: Biooil production from fast pyrolysis of biomass has aroused great attentions and interests extensively in recent years because the excess consumption of fossil fuels and high efficiency of biomass pyrolysis technique. The product of fast pyrolysis of biomass, biooil, has deleterious properties of high viscosity, thermal instability, corrosiveness and chemical complexity, which results in many obstacles to their applications. A novel upgrading process, selective esterification over solid acid catalysts, were suggested. With model compounds of acetic acid and ethanol reacted to get ethyl acetate, solid acid catalysts 40％SiO/TiO2SO42－was selected as the best one for esterification activity. Upgrading of biooil over this solid acid catalyst in the subsequent experiment was investigated. The heating value increases by 50.7%. Dynamic viscosity is only one tenth of that of the original. Density of biooil is lowered by 22.6%. GC-MS analysis shows that organic acids are converted to esters such as formate, acetate et al over the solid acid by undergoing catalytic esterification. All of those proved that the properties of biooil are improved. However, the dehydration characteristic of 3A molecular sieve is not good and it has little effect on the properties of acidity, density and viscosity.