This study aimed to produce phenolic formaldehyde (PF) adhesives using the liquefaction product of bagasse lignin (LPBL) as a partial substitute for petroleum-based phenol. Lignin was extracted from bagasse using 93% acetic acid solution and was rapidly degraded in hot-compressed water by microwave heating using oxalic acid as catalyst. The liquefaction yield reached 78.69% under the optimal reaction condition. Gas chromatography–mass spectrometry (GC/MS) analysis showed that the main chemical compounds of the liquefaction product included mono-substituted and bis-substituted phenols, such as 2,6-dimethoxyphenol, 4-hydroxybenzaldehyde, and so on. The LPBL was employed to replace a portion of phenol at varying ratios from 0 to 20 wt % in the preparation of PF adhesives. The molecular weight, viscosity, and adhesive strength of LPBL-PF adhesives were found to be lower than those of pure PF adhesives. With the phenol replaced by LPBL up to 20%, the viscosity and adhesive strength of the resin were 4.046 Pa s and 1.017 MPa, respectively.