Abstract:  Esterification with microwave, as a new method to upgrade crude bio-oil, was brought forward according to the composition characteristics of bio-oil. Crude bio-oil was upgraded in ethanol using the 732^# cation exchange resin and ZnCl₂ exchanged resin as catalysts and using the microwave as heating resource. The results show that the ZnCl₂ exchanged resin performs a higher activity duing the upgrading process and the heating by microwave can effectively promote the upgrading process compared to traditional water-bath heating.The analyzed results by GC-MS show that the components of upgraded bio-oil are optimized greatly. Under the best reaction conditions the acetic acid conversion gets to 70.47% and the adverse components such as acids, ketones, aldehydes and phenols in crude bio-oil are removed during upgrading process. The kinematical viscosity of upgraded bio-oil decreases by 36.29% and the density decreases by 19.4% compared to that of crude bio-oil. While the heating value of upgraded bio-oil increases by 48.43%, which indicate that the quality of upgraded bio-oil is obviously improved.