Sodium-ion batteries (SIBs) are not only cheaper to produce than lithium-ion batteries, but the reserves of sodium in the world are also more uniform and abundant. Thus, efforts are being made to utilize sodium-ion batteries as next-generation large-capacity energy-storage devices. Sb-based anode materials have emerged as a popular alloying material for SIB owing to their high theoretical capacity. However, Sb exhibits the problem of capacity fading owing to excessive volume expansion (approximately 390%). SiOC is a buffer material that has been investigated in terms of its ability to overcome these disadvantages; however, SiOC has the disadvantage of containing a fixed and limited free-carbon domain. Here, high free-carbon contained in Sb/SiOC composites (HFC-Sb/SiOC) was easily synthesized by the heat treatment of divinylbenzene (DVB), a liquid carbon source, with silicone oil and Sb acetate. Sb nanoparticles were uniformly embedded in DVB-modified SiOC with increased free-carbon domains. This composite material showed cycling stability (344.5 mAh g(-1)after the 150 cycles at 0.2 C) and outstanding rate properties (197.5 mAh g(-1)at 5 C) as the SIB anode. The enhanced electrochemical performance is result from the increased free-carbon domains in the SiOC matrix caused by the addition of DVB, which makes the characteristics of the SiOC material softer and more elastic, suppressing volume changes and enhancing the electrical conductivity.