The method of this invention for producing electrolyzed water containing ozone employs an apparatus for producing electrolyzed water from a liquid. The apparatus has two plate electrodes facing each other, a D.C. power source for applying a D.C. voltage across the electrodes and a control circuit for changing a polarity of the electrodes alternately. The method includes the step of producing electrolyzed water by changing the polarity, while a liquid is caused to flow in a flow passage between the electrodes, and the polarity is changed at an interval of time T as defined by formula (10):0.5nullTnull(null)null(L/V)nullnull(10)wherein; V: Velocity of flow of the liquid in the flow passage (cm/sec.), and L: Length of the electrodes as measured in the direction of flow of the liquid (cm).