Abstract： Objective　To study the roles of fibronectin(FN) played in rat pulmonary fibrosis. Methods　The dynamic change of FN was observed in bleomycin-induced rat pulmonary fibrosis using immunohistochemical technique. Northern blot analysis and immunocytochemistry techniques were performed to detect the expression of typeⅠ，Ⅲ procollagen mRNA and their relevant proteins in cultured rat pulmonary fibrobasts(PFbs) after FN treatment. Results　(1) The pulmonary tissue of rats which received bleomycin showed continuously strong positive reaction with anti-FN. (2) The expression of typeⅠ，Ⅲ procollagen mRNA in rat PFbs enhanced at 2 h after FN treatment，and reached their peaks at 6 h，12 h respectively. The expression of typeⅠ，Ⅲ procollagen proteins detected by immunocytochemistry was also increased after the FN treatment (P<0.01). Anti-integrin α5 monoclonal antibody could partially inhibit the effect of FN on enhancing the expression of typeⅠ，Ⅲ procollagen in PFbs (P<0.05). Conclusions　FN could up-regulate the synthesis of typeⅠ，Ⅲ procollagen mainly by enhancing the transcriptions of procollagen genes.