Efficient and low-cost electrocatalysts for water splitting are essential for solar fuel production. Herein, we report that nanoarrays of CoP supported on carbon cloth are an efficient bifunctional catalyst for overall water splitting. The catalyst exhibits remarkable activity for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline media, delivering a current density of 10mAcm(-2) at an overpotential of 281mV for OER and 95mV for HER. During electrocatalysis, the surface of the CoP catalyst was covered with a layer of CoOx, which was the active species. However, the CoP core and the nanoarray morphology contributed significantly to the activity.