Endoscopic ultrasonography (EUS) has been developed for the diagnosis of various gastrointestinal diseases or extra-gastrointestinal diseases, and extended to interventional approach. In fields of mediastinal diseases, EUS is an effective diagnostic method for the staging of esophageal cancer, lung cancer and other mediastinal diseases. Recently, EUS guided fine needle aspiration or biopsy makes the histologic diagnosis possible in various mediastinal diseases, and would reserve many avoidable surgical cases.