Disclosed is a silicon-carbon composite for a negative active material of a lithium secondary battery, including carbon nanofibers and silicon particles, wherein the silicon particles are coated with amorphous silica. In the silicon-carbon composite of the invention, silicon is provided in the form of a composite with carbon fibers and the surface of silicon particles is coated with amorphous silica, thereby reducing volume expansion upon lithium ion insertion and exhibiting superior ionic conductivity and electrical conductivity to thus maintain high capacity, and also, amorphous silica-coated silicon is positioned inside the carbon fibers having a one-dimensional structure, thus ensuring a large specific surface area and a stable composite structure.