A novel anode material for sodium ion batteries - nanosized CoP particles - was synthesized by a facile and productive ball-milling method. The CoP was tested as an anode candidate for sodium ion batteries. It delivered a high initial specific capacity of 770 mAh g−1, and excellent rate capability, demonstrating that CoP is a promising anode candidate for sodium ion storage. Ex-situ X-ray photoelectron spectroscopy and scanning transmission electron microscopy were carried out to investigate the sodium storage mechanism of CoP.