Provided is a method for operating a redox flow battery, the method including a step of mixing a predetermined volume of a positive electrolyte and a predetermined volume of a negative electrolyte at a predetermined period, in which the predetermined period is time x selected from a range of 320 hours or less, the predetermined volume is y % of a storage volume set for one of a positive electrolyte tank and a negative electrolyte tank, y is equal to or higher than a value represented by y=0.01%×x, when x is selected from a range of 30 hours or less, y is equal to or lower than a value represented by y=0.9%×x, and when x is selected from a range of more than 30 hours to 320 hours, y is 27.0% or less.