A　major　challenge　in　the　nitride-based　materials　for　photocatalytic　oxidation　reaction　is　their　low　stability　under　oxidizing　and　acidic　environment.　To　solve　these　problems,　highly　crystallized　hexagonal　boron　carbon　nitride　(BCN)　with　more　homogeneous　mixing　of　B,　C,　and　N　atoms　is　achieved　by　pyrolysis　of　precursor　materials　in　the　presence　of　NaOH　as　a　crystallization　promoter.　The　high　crystallinity　and　chemical　homogeneity　features　of　the　fabricated　BCN　reduce　the　structural　defects　and　accelerate　the　interfacial　charge　transfer　and　separation,　thus　inhibiting　the　self-oxidation　and　endowing　it　with　a　superior　oxidation　resistance.　With　these　prominent　advantages,　the　highly　crystallized　BCN　exhibits　markedly　enhanced　photocatalytic　activity　and　long-term　anticorrosion　stability　under　oxygen　and　self-generated　acidic　condition,　far　beyond　polycrystalline　BCN.　This　work　offers　new　insights　into　the　catalyst　design　of　crystalline　BCN　and　demonstrates　its　great　promise　for　solar　energy　applications.　©　2022　Wiley-VCH　GmbH.