Highly phenol substituted bio‐oil–phenol–formaldehyde (BPF) adhesives were prepared via the phenolization‐copolymerization method, in which furfural was used as a novel crosslinking agent to improve the bonding performance. The effects of bio‐oil percentage, furfural content, curing temperature, and pressure on the performance of BPF adhesives have been studied in detail. A BPF adhesive with 75% bio‐oil percentage and 15% furfural loading (named 75BPF_15) was synthesized, which was cured at 180 °C and 4 MPa. Compared to the conventional phenol–formaldehyde adhesive, the wet tensile strength of 75BPF_15 adhesive reached 2.84 MPa, which was significantly higher than the 1.54 MPa of PF. A possible mechanism of BPF adhesives crosslinked with furfural is proposed. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 46995.