A novel magnetic g-C₃N₄/CoFe₂O₄ nanocomposite was successfully synthesized by a simple hydrothermal method and applied as a new graphene-like carbon nitride-based sonocatalyst for sonodegradation of pollutant dyes. The as-prepared samples were characterized by using X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), vibrating sample magnetometry (VSM), X-ray photoelectron spectroscopy (XPS), UV-visible diffuse reflectance spectroscopy (DRS), BET surface area measurements and photoluminescence (PL) spectroscopy. The results indicate that the nanocomposite sample is composed of spherical CoFe₂O₄ nanoparticles adhered to g-C₃N₄ naosheets. The g-C₃N₄/CoFe₂O₄ nanocomposites were used as a new magnetically separable sonocatalyst in H₂O₂-assisted sonodegradation of methylene blue (MB), rhodamine B (RhB) and methyl orange (MO) dyes in aqueous media. The results showed complete degradation (ca. 100%) of dyes within short times (30–35 min). The sonocatalytic activity of graphitic carbon nitride (g-C₃N₄) was greatly enhanced with CoFe₂O₄ modification. Trapping experiments indicated that the g-C₃N₄/CoFe₂O₄ nanocomposites serves as a generator of hydroxyl radical (˙OH) via activation of H₂O₂ for degradation of dyes under ultrasound irradiation. Furthermore, the magnetic sonocatalyst can be separated from solution by an external magnet and reused several times without observable loss of activity. The possible mechanism of sonocatalytic activity was also proposed according to experimental results.