α-Si3N4 K15nanorods with 20-80 nm width were synthesized by carbothermal reduction of SiO with amorphous activated carbon (AAC) as a reductant. Microstructural characterization of the synthesized nanorods was carried out by high resolution transmission electron microscopy (HRTEM)and energy dispersive X-ray analysis. Many Si3N4 nanorods were found to be twisted. Each twisted nanorod contained several straight Si3N4 parts. The straight parts had the rod axes orientated along the〈1010〉direction, which is the closest packing direction of a-Si3N4. There were two kinds of joints between the two adjacent straight Si3N4 parts. Formation mechanism of the Si3N4 nanorods is discussed.