The present invention provides electrolyte that can suppress reduction of battery efficiencies and capacities with increased cycles of charge/discharge of the battery, a method for producing the same, and a redox flow battery using the same electrolyte. The redox flow battery uses the electrolyte having a NH.sub.4 content of not more than 20 ppm and a relation of Si concentration (ppm).times.electrolyte quantity (m.sup.3)/electrode area (m.sup.2) of less than 5 ppmm.sup.3/m.sup.2. By limiting a quantity of contaminants in the electrolyte, a clogging of carbon electrodes to cause reduction of the battery performances with increased charge/discharge operations can be suppressed.