The industry application of bio-oil has been constrained due to its poor fuel properties. Ethyl acetate, acetone, n-octanol, and polyethylene glycol 400 as mutual solvents as well as ultrasonic treatment were employed to improve the chemical and physical properties of heavy bio-oil. When the ratio of n-octanol to heavy bio-oil was 3:1, ultrasonic power was 150 W, and exposure time was 12 min, the viscosity (40 degrees C) of heavy bio-oil decreased from 1244.60 to 6.05 mm(2).s(-1), the heat value increased to 41.02 MJ.kg(-1), and the pH increased to 6.23. Thermogravimetric analysis (TGA) results showed that no change is obvious in the TG curve for some of the blends after 60 days. Moreover, Fourier transform infrared spectroscopy (FT-IR) effectively verified that some of the blends were stable after 60 days and some were not, but no stratification was observed. FT-IR and TGA are fast and easy tools to examine the stability and homogeneity of the blends.