Objective An electron microscopic study was carried out to examine the pulmonary changes of rats suffering from acute respiratory distress syndrome(ARDS).Methods ARDS animal disease model was developed by means of paraquat(PQ) toxicant exposure.The pulmonary tissue was examined by electron microscopy.Results The pulmonary alveolar wall of normal rats was thin and intact.Lamellar bodies in the type II pneumocytes did not show any sign of evacuation.Pathological changes caused by pneumonic damage of pulmonary tissue in ARDS rats were observed.Conclusion Various pathological changes caused by ARDS pulmonary damage can be observed under the transmission electron microscope.The evacuation of substance from lamellar bodies in the type II pneumocytes can be seen as a characteristic pathological change caused by ARDS.Such lamellar body alteration in type II pneumocytes perhaps provides an important basis for the judgement of ARDS attack.