A core-shell structured Si nanoparticles@TiO2-x/C mesoporous microfiber composite has been synthesized by an electrospinning method. The core-shell composite exhibits high reversible capacity, excellent rate capability, and improved cycle performance as an anode material for Li-ion batteries. Furthermore, it shows remarkable suppression of exothermic behavior, which can prevent possible thermal runaway and safety problems of the cells. The improved electrochemical and thermal properties are ascribed to the mechanically, electrically, and thermally robust shell structure of the TiO2-x/C nanocomposite encapsulating the Si nanoparticles, which is suggested as a promising material architecture for a safe and reliable Si-based Li-ion battery of high energy density.