The object of this invention is a method by which arsenic is removed from sulfuric acid solution, in which the sulfuric add concentration is at least 300 g/l, at a temperature of 50-105.degree. C. by reducing the arsenic in the solution with the aid of sulfur dioxide. The arsenic trioxide produced is crystallized from the sulfuric acid solution by cooling. The method is particularly suitable for use in connection with the electrolytic refining of metals, as in copper refining.