Polyhydric alcohols are known as excellent solvents for converting the main components of lignocellulose into liquefied products. However, the substances that precipitate in water include not only lignin, but also humins, especially when the lignocellulosic raw material has a high content of carbohydrates. Therefore, the main objective of this study was to investigate the composition of water-insoluble solids from the liquefaction of oil palm trunk using the solvent polyethylene glycol (PEG)/glycerol (4:1, w/w) and by using sulfuric acid as the catalyst. The results showed that the water-insoluble components had a relatively higher average molecular weight and polydispersity than those of the water-soluble components and liquefied products. The production of sugar monomers during liquefaction led to the condensation of furan products (hydroxymethylfurfural and furfural) to form humins. In this case, the humins were incorporated with the lignin and liquefying reagent.