Mycoplasma pneumoniae (M. pneumoniae) pneumonia is usually considered as a benign disease, but in rare cases, the disease is fatal. Fatal cases requiring mechanical ventilation and many extrapulmonary complications have been reported. Cases accompanied with obliterative bronchiolitis also have been reported. Two cases of M. pneumoniae pneumonia with obstructive ventilatory disturbance were reported. In both cases clinical diagnosis of M. pneumoniae pneumonia was confirmed by a rise in the complement fixation antibody titer, a rise of the cold hemagglutinin titer and isolation of M. pneumoniae from sputum and pharynx. In one case we performed transbronchial lung biopsy (TBLB). The lung biopsy specimen showed bronchiolitis, so histological findings were thought to be compatible with ventilatory function. In both cases arterial oxygen pressure (PaO2) was below 60 Torr, by administration of erythromycin (EM) and adrenocorticosteroids, chest X-ray findings, atrial blood gas analysis findings and ventilatory function were improved.