Herein, we report for the first time the highly efficient degradation of 2,4-dichlorophenol (2,4-DCP) over CeO2/g-C3N4 composites (xCeO/CN) prepared via wet-chemical solution method. It is shown that the resultant nanocomposites with a proper mass ratio percentage (15%) of CeO coupled exhibit greatly enhanced visible-light activity for 2,4-dichlorophenol (2,4-DCP) degradation compared to the bare g-C3N4. From photoluminescence (PL) and Fluorescence (FL) results, it is suggested that enhanced photo-degradation is attributed to the significantly improved charge separation and transfer as a result of the proper band alignments between g-C3N4 and CeO components. Further, from radical trapping experiments, it is confirmed that hydroxyl radicals (OH) are the predominant oxidants involved in the degradation of 2,4-DCP over CeO/CN composites. Furthermore, a possible reaction pathway and detailed photocatalytic mechanism for 2,4-DCP degradation is proposed mainly based on the detected liquid chromatography tandem mass spectrometry (LC-MS) intermediate products, that readily transform into CO2 and H2O. This work would help researchers to deeply understand the reaction mechanism of 2,4-DCP and would provide feasible routes to fabricate g-C3N4-based highly efficient photocatalysts for environmental remediation. Copyright © 2018 Elsevier B.V. All rights reserved.