Silicon nanowires (SiNWs) have been fabricated by chemical vapor deposition at ambient pressure using C SiCl4 as a silicon source and mesophase carbon microbead powder as a substrate without any templates and/or metal catalysts. The SiNWs have a crystalline core with a very thin amorphous SiOx sheath. The obtained SiNWs are homogeneous with average diameters below 50 nm and lengths up to micrometers. Temperature and time effects on the growth of SiNWs were systematically studied. Higher reaction temperatures and longer reaction times resulted in larger diameters and higher yields of SiNWs. SiNWs with a better crystallinity can be obtained at higher temperatures and longer reaction times. The obtained SiNWs were characterized by field-emission scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and transmission electron microscopy.