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A two-step treament was developed to obtain purified betulin from birch bark.The birch bark was first extracted using alkaline ethanol solution,and then the extract was purified by ethyl acetate / water two phase solvent system.The effect of the concentration of NaOH in alkaline ethanol solution on the purity of betulin was evaluated,results showed that optimum concentration is 0.63 mol·L-1,and the purity of obtained product is 86,65%.