Al₄B₂O₉ whiskers on the surface of porous SiC substrates were fabricated by chemical reactions between Al(NO₃)₃ and H₃BO₃, which is a facile method to prepare cilia-like microstructure for gas–solid separation. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy were employed to investigate the structural morphology and phase compositions. Al₄B₂O₉ whiskers with nanometer-sized diameters and micrometer-sized lengths grew on the surface of SiC substrates, and a self-catalytic mechanism was used to explain Al₄B₂O₉ whisker growth.