The B 4 C nanowires can be easily fabricated by employing an activated carbon, boron and Ni(NO 3 ) 2 whereas almost no B 4 C nanowires can be obtained if activated carbon is replaced by pure carbon. The analyses show that there are Si and Al impurities in the activated carbon, and both Si and Ni are critical to the growth of the B 4 C nanowires. Additionally, the yield of the B 4 C nanowires is greatly increased if the B 4 C nanowires are grown by the carbon nanotubes-confined method when Si is introduced. The mechanism of the Si enhanced growth of B 4 C nanowires is discussed.