Silicon/disordered carbon Si-DC nanocomposites have been synthesized by high-energy ballmilling of Si-sucrose and silicon-polyvinyl alcohol followed by pyrolysis under argon flow. The exact disordered carbon content in the as-prepared Si-DC nanocomposites was determined by thermogravimetric analysis for the first time. Based on the thermogravimetric analysis, X-ray diffraction, Raman, and cyclic voltammetric results, we believe that carbon distribution on the Si particles in Si-DC nanocomposite using PVA as the carbon source is more uniform and has higher efficiency than that using sucrose as the carbon source, under the same preparation conditions. The carbon content and the starting polymers significantly affect the electrochemical performance of the Si-DC nanocomposites. The optimized Si-DC nanocomposite anode demonstrated a reversible capacity of 754 mAh/g within 20 cycles.