SiC nanorods with 20-100 nm diameter and 10–100μm length were synthesized by reaction between SiO and amorphous activated carbon (AAC) at 1380℃. Microstructural characterization of the SiC nanorods was carried out by high resolution transmission electron microscopy (HRTEM) and energy dispersive spectroscopy (EDS). The SiC nanorods grow on either a chain or from facets of SiC nanoparticles. They are usually straight and preferentially orientated along the [111] direction. Branching phenomenon exists for these nanorods. Typical SiC nanorod tip was analyzed by HRTEM image and EDS analysis. Based on an experimental analysis, a formation mechanism is proposed to explain the microstructural characterization of the SiC nanorods.