Novel SiOC nanocomposites were successfully synthesized from commercial silica sol and sucrose via a simply designed route. The formation of SiOC nanocomposites was studied using thermogravimetry and differential scanning calorimetry. The synthesized nanocomposites were characterized by Fourier transform infrared spectroscopy, x-ray fluorescence spectrometer, x-ray photoelectron spectroscopy, x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results indicate that the synthesized composites are amorphous in nature and homogeneous with the microstructure of close packed SiO(2) and carbon at nanoscale. The SiOC nanocomposites exhibit very high reactivity and can be annealed to produce SiC nanocrystals at 1200 degrees C which is about 300 degrees C lower than the value obtained by thermodynamic calculation. Ultra-large-scale beta-SiC nanowires with high quality were prepared by directly annealing the synthesized SiOC nanocomposites at 1500 degrees C under Ar atmosphere, where the yield of SiC nanowires was up to 59%. The SiC nanowires grow along the [111] direction with highly uniform diameters of about 100 nm. Experimental results indicate that the close contact between SiO(2) and carbon at nanoscale plays a vital role in the high yield of SiC nanowires. The present work provides an efficient strategy for the large scale production of high-quality SiC nanowires.