Single-crystalline B-C-N nanorods were prepared at 500 °C and less than about 20 MPa. Results from X-ray powder diffraction (XRD) and selected-area electron diffraction (SAED) measurements suggest that the synthesized single-crystalline B-C-N is of tetragonal structure and its lattice constants are a = 7.12(5) A and c = 3.57(3) A. The nanorods all are very straight, and the ratios of length to diameter are between 5 and 30. High resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM) observations confirm the well-defined nanorods grown preferentially perpendicular to the [220] direction develop tetragonal morphologies. The energy-loss spectroscopy (EELS) and energy-dispersive X-ray (EDX) elemental mapping confirm that the nanorod is composed of B, C, N, and a trace of oxygen, and its stoichiometry is determined to be close to BC 2 N. First-principles calculations confirm that the as-prepared sample is superlattice phase of β-BC 2 N phase with defects of the C N ' and the ON'. In addition, it is a semiconductor material with a direct energy band gap 1.21 eV. The calculated hardness is comparable to that of diamond.