Provided are a redox flow battery (RF battery) in which a positive electrode electrolyte and a negative electrode electrolyte are supplied to a battery cell including a positive electrode, a negative electrode, and a membrane, to charge and discharge the battery, and a method of operating the RF battery. The positive electrode electrolyte contains a manganese ion, or both of a manganese ion and a titanium ion. The negative electrode electrolyte contains at least one type of metal ion selected from a titanium ion, a vanadium ion, a chromium ion, a zinc ion, and a tin ion. The RF battery can have a high electromotive force and can suppress generation of a precipitation of MnO2 by containing a titanium ion in the positive electrode electrolyte, or by being operated such that the positive electrode electrolyte has an SOC of not more than 90%.