Development of low-cost, high performance and stable non-noble electrocatalysts with both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activities for overall water splitting is essential for future energy supply. Herein, for the first time, a facile and ultrafast synthetic method has been reported to fabricate nickel sulfide (Ni3S2) films on Ni foam (Ni3S2/NF) as efficient bifunctional electrodes for overall water splitting through direct dropping of mercaptoethanol solution followed by annealing at 300 °C for only 50 s. Thanks to the integrated three-dimensional (3D) configuration, the obtained Ni3S2/Ni foam exhibits excellent activity and stability for HER and OER with low overpotentials of 131 and 312 mV, respectively, to attain a current density of 10 mA cm-2 in alkaline media. Ni(OH)x species formed on the Ni3S2 surface serves as the actual catalytic site during OER reaction. Given the well-defined bifunctionality, an overall water-splitting device using two identical Ni3S2/NF electrodes delivers a current density of 10 mA cm-2 at a low cell voltage of 1.68 V in an alkaline water electrolyzer. This approach is promising as a simple method for depositing a wide range of useful transition metal sulfide electrocatalysts on corresponding metal substrate bifunctional electrodes for overall water splitting, shedding some light on the development of functional materials in energy chemistry.