The present invention relates to a redox flow battery, and more particularly, to a redox flow battery which is charged and discharged by supplying a positive electrolyte and a negative electrolyte to a battery cell using an active material containing vanadium and a cation exchange membrane, in which the positive electrolyte and the negative electrolyte contain vanadium ions as active ions, the difference in volume between the positive electrolyte and the negative electrolyte is maintained at 10% or less, and the total concentration of anions in the negative electrolyte is higher than the total concentration of anions in the positive electrolyte, whereby the transfer of water in the battery is controlled and a change in the volume of the electrolytes is minimized.