Two novel inorganic–organic hybrid materials, namely, (NH₄)₂CuMo₈O₂₆(C₁₀H₈N₂)₂ (1) and Mo₈O₂₆(C₁₀H₁₀N₂)₂(C₁₀H₈N₂)·2(H₂O) (2) have been synthesized based on β-octamolybdate cluster and 4,4′-bipyridine (4,4′-bpy) ligand under solvothermal conditions. Their structures have been determined by single-crystal X-ray diffraction analyses and characterized by FT-IR, atomic absorption spectroscopy, powder X-ray diffraction (PXRD) and thermogravimetric analysis (TGA). In addition, microcrystals of 1 were used to synthesize its nanocrystals via an ultrasound-assisted top-down method. The nanocrystals were characterized by scanning electron microscopy (SEM), PXRD and FT-IR analyses. The prepared hybrid materials have been proved to be active heterogeneous catalysts for catalytic wet air oxidation (CWAO) of some dyes under mild conditions. Leaching experiments showed that the catalysts had good stability under the reaction conditions and could be easily recycled and reused after a simple treatment.