The co-liquefaction of mixtures of sugarcane bagasse and high density polyethylene (HDPE) in ethanol under subcritical and super-critical conditions was studied with the objective of finding optimal process conditions for bio-oil yield and overall conversion. Taguchi method was employed to design with 9 experiments to find the effect of 4 independent variables (temperature, reaction time, biomass to plastic composition and solvent-to-biomass ratio) on the co-liquefaction of plastic and biomass for total conversion and bio-oil yield. The optimal results showed 60 % conversion with bio-oil yield 32.3 % having HHV of bio-oil 29.6 MJ/kg respectively. The predicted model indicated a good fit with that of experimental data. Furthermore, detailed characterizations of bio-oils were carried out such as higher heating value (HHV), chemical composition, NMR analysis, elemental analysis, FTIR and thermogravimetric analysis. The co-liquefaction of sugarcane bagasse and polyethylene was found effective to improve the qualitative and quantitate features of products from the biomass. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.