This study was undertaken to investigate paraquat-induced pulmonary injuries and effects of colchicine on pulmonary fibrosis by paraquat. Fifteen Sprague-Dawley rats were intraperitoneally injected 10 mg/kg of paraquat and repeatedly with 2 days interval. Another 15 rats were injected paraquat as same manner and simultaneously injected 10 mg/kg of colchicine in a week. Five rats in each group were sacrificed 1, 2, and 4 weeks after initial injections, and lungs extracted were observed by light and electron microscopes. On light microscopy, there was mild infiltration of neutrophils, macrophages, and lymphocytes in alveolar spaces and walls at 1 week after paraquat injection. The cellularity of alveolar wall was increased with time. However, the cellularity was not so prominent in paraquat and colchicine simultaneously injected group. On electron microscopy, there was marked swelling or excoriation of type I epithelial cells and alveolar capillary endothelium with infiltration of neutrophils, macrophages and monocytes, and lymphocytes in alveolar walls. Such findings were persisted with time. In addition, fibroblastic proliferation and deposition of collagen fibers were prominent at 4 weeks after paraquat injection. Fibrosis also occurred at 4 weeks after paraquat and colchicine simultaneous injection. It was not proninent than that of paraquat injected group. According to the above result, it would be concluded that the type I pneumocytes and alveolar capillary endothelial cells are most vulnerable on paraquat poisoning, and that the colchicine is effective on inhibition of paraquat-induced pulmonary fibrosis.