PURPOSE: A sterilizing device for a water purifier is provided to sterilize purified water by directly destructing a cell membrane of bacteria existing on an upper space of a reservoir and purified water of a reservoir by emitting ozone gas and dissolved ozone to the reservoir. CONSTITUTION: A sterilizing device for a water purifier includes a flow sensor(110) and an electrolysis cell(100) between a water purifying filter(2) and a water supply float valve(3). When a flow sensor detects a flow of purified water, ozone gas and dissolved ozone are produced on the surface of a positive electrode by electrolyzing purified water flowing around an electrode. The purified water in a reservoir(4) and an air layer on the top of a reservoir are sterilized with the dissolved ozone and the ozone gas.
