The present invention relates to use of Ulinastatin and its pharmaceutical composition for treating and/or preventing Severe Acute Respiratory Syndrome (SARS). Ulinastatin is effective for treating and/or preventing SARS, particularly Acute Lung Injury (ALI) or Acute Respiratory Distress Syndrome (ARDS). Ulinastatin is generally used as the pharmaceutical composition, preferably in the form of freeze-dried powder or aqueous solution for injection.