Magnesiothermic reduction of silicon oxide (SiO2) is thought to be an effective method for preparing nanostructured silicon (Si). However, the magnesiothermic reduction can hardly maintain the original shape of the SiO2 due to the harsh reaction condition. Carbon coating is an efficient strategy to prevent the original structure collapse and improve its conductivity, while the by-product silicon carbide (SiC) is prone to form due to the overheating phenomenon during the process, which is useless to the Li-ion storage. Herein, potassium iodide (KI) is used as heat scavenger for the first time to control the formation of SiC, in which the melt of KI can absorb excess heat during the harsh reduction process. Ideally, hollow Si/C nanospheres and nanorods with little content of SiC are successfully synthesized by the KI-assisted magnesiothermic reduction from carbon coated SiO2 precursors. These novel hollow Si/C nanospheres and nanorods endow it with an excellent electrochemical performance as anodes for Li-ion battery. In detail, Si/C nanospheres achieve a specific capacity of 1792 mAh g(-1) after 100 cycles at 1 A g(-1), and 1271 mAh g(-1) even at a high current density of 3 A g(-1) after 200 cycles. This novel strategy provides an effective and facile way to reduce SiC generation during magnesiothermic reduction reaction and can be applied to obtain Si/C composites with various morphology.