Mycoplasma pneumonias is one of the most common etiological agent causing community acquired interstitial pueumonia. The pathophysiologic mechanism of the disease is based on a unique gliding motility, adhesion to respirator epithelial cells and the
induction of a pathological hyperstimulation of cellular response mechanism of the host in addition to the direct invasion. We reported a 7-year-old child with mycoplasma pneumonia after undergoing unrelated bone marrow transplantation for the treatment
of juvenile myelomonocytic leukemia(JMML). He developed severe productive cough and dyspnea about three weeks after UBMT. After serologic study of actue and convalescent phase, mycoplasma pneumonia was confirmed and respiratory symptoms was improved
after roxithromycin therapy. Because he was reversibly isolatd and had no contact with community, there was a possibility of endogeneous reactivation. This case suggests that when the bone marrow transplant recipient manifests respiratory syptoms
such as cough and dyspnea, mycoplasma pneumonia should be included as one of the possible causative disease in addition to CMV pneumonitis of pneumocystis carinii pneumonia.