To observe the expression of pulmonary surfactant-associated protein D (SP-D) during human fetal lung development.Human fetal lung tissues from 11- to 36-week-old fetuses were assayed for lung maturity with HE staining and SP-D expression by means of immunohistochemistry.SP-D expression was located in the bronchial epithelium and alveolar epithelial type II cells(AEC II) of the lung tissues since the 12th week, and gradually increased during the canalicular to saccular stages with fetal development, at the point of which SP-D-positivity began a shift from the proximal bronchial epithelium to AEC II , and evidently located in the alveoli from the advanced stage of lung development till postnatal stage.SP-D expression gradually intensifies with the maturation of the fetal lungs, and SP-D-positive cells begin to be detected in the bronchial epithelium and finally in AEC II.