The interstitial lung diseases(ILD) comprises a large, heterogeneous group of disorders characterized by derangement of alveolar walls and alveolar capillary unit causing restrictive pulmonary dysfunction and disordered gas exchange. It is rare, especially in children, and the opinions on investigation and treatments are controversial. The classification of adult ILD is applied to that of children. But considering occurrence during the developing state of lung and immune systems, we should be more cautious because the clinical manifestations and prognosis will be different from those of adults. In 1995, Katzenstein named a unique type of ILD, chronic pneumonitis of infancy (CPI) for the first time. CPI is characterized by marked alveolar septal thickening, striking type II pneumocyte hyperplasia, and eosinophilic alveolar exudate containing numerous macrophages. We report a 14 month-old girl, who had continuing respiratory difficulty and cyanosis after upper respiratory infection, could not sustain oxygen saturation and was finally diagnosed as CPI by histologic examination.