Hollow nanospheres are desirable to resolve the volume expansion of red phosphorus anodes for sodium-ion batteries. Here, we developed a mild molten salt method to prepare hollow red phosphorus in the NaCl-KCl-AlCl3 system by using the Kirkendall effect. As an anode for sodium-ion batteries, the prepared hollow nanospheres exhibit a highly reversible capacity of 624 mA h g-1 at 4.0C and 737 mA h g-1 at 1.0C even after 600 cycles with a low capacity fading rate of 0.06% per cycle.