An electrolyte for a redox flow battery has a total concentration of arsenic ions and antimony ions of 15 mass ppm or less. In an example of the electrolyte for a redox flow battery, preferably, the concentration of the arsenic ions is 10 mass ppm or less. In another example of the electrolyte for a redox flow battery, preferably, the concentration of the antimony ions is 10 mass ppm or less.