Abstract: The excessive FeCl₃ solution is added into the analytical sample.The metallic aluminiun (MAl) in the sample is made to oxidizing-reducing react with Fe³⁺ by means of stirring,resulting Al³⁺ coming into solution.The Al₂O₃ doesn't react,retains in the precipitate.After fluorine is removed and calcium,magnesium and iron separated from the Al³⁺ bearing filter liquor,the MAl content is determined with CuSO₄ titrimetry,the MAl content is subtracted from the total Al content,then the Al₂O₃ content is calculated.