Phosphorization engineering is an alternative method to explore highly efficient electrocatalysts for water splitting. Herein, a heterostructure consisting of Ni2P and Ni3S2 supported on commercial nickel foam (Ni3S2-Ni2P/NF) was prepared through the conversion of some Ni3S2 molecules into Ni2P by phosphorization engineering. Electrochemical tests revealed that the partial phosphorization of Ni3S2 effectively enhanced the catalytic activity of the host electrocatalyst towards the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in 1 M KOH; in particular, the Ni3S2-Ni2P/NF electrode exhibited the current density of 50 mA cm-2 at the very low OER overpotential of 287 mV and needed the low overpotential of 130 mV to afford 10 mA cm-2 for the HER. Moreover, the alkaline electrolyzer assembled by two Ni3S2-Ni2P/NF electrodes could deliver 10 mA cm-2 at the low voltage of 1.58 V and exhibited excellent durability during electrolysis for 15 h. Therefore, our study opens up an attractive fabrication strategy for highly active heterostructure electrocatalysts.