Abstract: Biomass-derived platform molecules, such as furfural, are abundant and renewable feedstock for valuable chemical production. It is critical to synthesize highly efficient photocatalysts for selective oxidation under visible light. The Er@K-C₃N₄/UiO-66-NH₂ catalyst was synthesized using a straight-forward hydrothermal technique, and exhibited exceptional efficiency in the photocatalytic oxidation of furfural to furoic acid. The catalyst was thoroughly characterized, confirming the effective adjustment of the band gap energy of Er@K-C₃N₄/UiO-66-NH₂. Upon the optimized reaction conditions, the conversion rate of furfural reached 89.3%, with a corresponding yield of furoic acid at 79.8%. The primary reactive oxygen species was identified as ·O₂ ⁻ from ESR spectra and scavenger tests. The incorporation of Er and K into the catalyst enhanced the photogenerated carriers transfer rate, hence increasing the separating efficiency of photogenerated electron-hole pairs. This study expands the potential applications of rare earth element doped g-C₃N₄ in the photocatalytic selective oxidation of furfurans.