Si3N4 nanowires and SiO2 amorphous nanowires with diameters of 10-70 and 10-300 nm, respectively, have been synthesized by heating Si powders or Si/SiO2 Mixtures with or without metal catalyst at 1200 degreesC at ambient pressure. It is found that the reactant gases (N-2 Ar and NH3) affect the yields and morphologies of the products, and the metal catalysts are not necessary in growth of the Si3N4 and SiO2 nanowires. High resolution electron microscopy (HREM) and electron energy loss spectrum (EELS) reveal that the Si3N4 nanowire is a single crystal covered by an amorphous SiO2 layer. The growth mechanism is assumed to be a vapor-solid (VS) process.