Abstract: Upgradation of bio-oil before utilization is desirable to obtain high grade fuel because of its drawbacks like high viscosity, low heating value, poor stability and high corrosiveness. Organic acids in bio-oils can be converted to their corresponding esters by catalytic esterification and this greatly improved quality of bio-oils. We selected 732 and NKC-9 type ion exchanger resins as esterification catalysts for upgrading bio-oil. The catalytic activity was first investigated by model reaction first. The esterification of bio-oil with methanol was conducted in a batch reactor. Acid numbers of upgraded bio-oil on 732 resin and NKC-9 resin were lowered by 88.54% and 85.95% respectively, which represents the conversion of organic acids to neutral esters; the heating values increased by 32.26% and 31.64% respectively; the H2O contents decreased by 27.74% and 30.87% respectively; the densities were lowered by 21.77% for both and the viscosities fell by approximately 97%. A fixed bed reactor was used for continuous catalytic esterification of bio-oil by 732 resin and the acid number remarkably decreased by 92.61％. The accelerated ageing test showed improvement of stability and the aluminum strip corrosion test showed reduced corrosion rate of bio-oil after upgradation.