Silicon-carbon (Si-C) composites with various weight ratios were prepared through heat treatment of water-soluble carboxymethyl cellulose (CMC) with Si nanoparticles synthesized by using an inductively-coupled plasma. Microstructures of the Si-C composites were thoroughly investigated by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and Raman spectroscopy. The results indicate that we obtained a micro-sized Si-C composite with homogeneously-distributed crystalline Si nanoparticles in an amorphous C-matrix. Pores, which were due to the volatilization of CO2 from CMC during heat treatment, was detected when the concentration of carbon was increased. The electrochemical properties of those Si-C composites for use as anode materials in lithium-ion batteries (LIBs) were also investigated. The C-matrix enhanced the capacity retention, as well as the rate capability of Si nanoparticles, due to the dense and homogeneous microstructures of the composite. The Si-C composites (7:3 weight ratio) retained a reversible capacity of > 1,000 mAh/g with a capacity retention of 88.9% even after 100 cycles. The reversible capacity ratio at a 1.5 C-rate was about 80% as compared with that at a 0.1 C-rate.