The synthesis of manganese oxide/graphitic carbon nitride (MnO2/g-C3N4) heterostructure was carried out via hydrothermal method. The obtained material was analyzed using several analytical techniques, including X-ray diffraction, Transmission Electron Microscope, UV–vis spectrophotometer, photoluminescence, and Scanning electron microscope, to determine its morphological, elemental, structural, and optical properties. The average size of the MnO2 nanoparticles is 33.6 ± 1 nm, with a range of 1.0 to 60 nm in TEM analysis. The optical bandgap of MnO2, g-C3N4, and MnO2/g-C3N4 nanocomposites were determined to be 1.75 eV, 2.75 eV, and 2.33 eV, respectively. The results indicate that the MnO2/g-C3N4 hybrid catalyst exhibits a degrading efficiency of 93.6 % in 120 min and great stability after five cycles. The mechanism of separating electron-hole pairs (e−/h+) that are created by photons and delaying the recombining of free charges has been widely reported.