The chemical composition of liquid products obtained from liquefaction of several agro-industrial wastes was analyzed and the effects of microwave treatments were investigated, evaluating changes in chemical composition, structure, and physical properties, looking forward to exploring new utilization routes or processing paths for these liquid products. Gas chromatography mass spectrometry (GC-MS) showed that the chemical components of liquefied products can be divided into several groups: furans, alcohols, and esters and acid derivatives. The microwave evaluation showed that irradiation at constant power levels affects the compositions of liquefied products. Fourier transform infrared (FT-IR) spectroscopic analysis showed increases in the absorption bands of carbonyl and CH groups, which suggests that microwaves induced more intensive oxidation of hydroxyl groups into carbonyl groups. Elemental analysis indicated higher carbon and lower oxygen contents and higher heat heating value (20 MJ/kg) in treated products with respect to untreated samples. The use of liquefied products as a new energy source has advantages such as their liquid state, convenient energy value, and renewability.