The g-C3N4/NaNbO3 photocatalyst was synthesized by simply calcining the mixture of NaNbO3 and melamine. The synthesized composite exhibits high photocatalytic performance in the selective oxidation of 5-Hydroxymethylfurfural (HMF) to 5-formyl-2-furancarboxylic acid (FFCA) when using water as solvent. The structure and composition of g-C3N4/NaNbO3 photocatalysts were characterized by TG, XRD, SEM, UV-Vis, FT-IR, and XPS methods, and the optical and electrochemical properties were investigated by EIS, PC, and PL techniques. O-center dot(2)- was inferred to be the primary active species in this process based on the active species trapping experiment. Heterostructure formation of g-C3N4/NaNbO3 composites efficiently promoted the separation of photo-generated electron-hole pairs and accelerated the electron transfer rate, thus reduced the formation of (OH)-O-center dot, and sequentially improved the selectivity of FFCA. The highest HMF conversion of 35.8% with FFCA selectivity of 87.4% was achieved on C/N-59.6 photocatalyst under the irradiation of visible light. The possible mechanism and reaction route were also proposed. (C) 2020 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.