We report two cases of bronchial asthma masked by hyperventilation syndrome. Case 1 was a 43-year-old woman. She had repeatedly visited the emergency room complaining of dyspnea and had been given a diagnosis of hyperventilation syndrome for 8 years. Initially, her symptom was only coughing, however, dyspnea gradually appeared. We suspected her symptoms were caused by bronchial asthma on the basis of her wheezes, and we established a diagnosis based on the results of the airway reversible test. Case 2 was a 24-year-old woman. She also had repeatedly visited the emergency room, supposedly because of hyperventilation syndrome over the long term. The airway reversible test revealed that she had features of asthma. After treatment for bronchial asthma, the asthma attacks subsided. After that, neither patient made any emergency visits. We should auscultate the respiratory sounds of patients with hyperventilation syndrome carefully. Additionally, we may as well apply the spirometries and the airway reversible test during a period of stability to a patient who has repeated hyperventilation attacks.