The effects of isoliensinine (IL), a bisbenzylisoquinoline alkaloid extracted from the Chinese traditional medicine seed embryo of Nelumbo nucifera Gaertn., on bleomycin (BLM)-induced pulmonary fibrosis in mice were investigated. Seventy-two male Kungming mice were divided randomly into eight groups as BLM-IL10, BLM-IL20, BLM-IL40, BLM-Sal, Sal-IL10, Sal-IL20, Sal-IL40 and Sal-Sal groups. BLM (0.1 mg in 0.05 ml saline per animal, once) or saline (0.05 ml per animal, once) was applied intratracheally, and IL (10, 20, 40 mg/kg) or saline was administered orally 3 times per day in the appropriate groups. Animals were sacrificed 14 days after intratracheal treatment. Lung tissue and serum superoxide dismutase (SOD) activity and malondialdehyde (MDA) levels, tumor necrosis factor alpha (TNF-alpha) and transforming growth factor beta 1 (TGF-beta (1)) were determined by biochemical measurements and immunohistochemistry. BLM treatment resulted in a significant increase of the hydroxyproline content and an obvious lung histological injury as compared to the Sal-Sal group. Administration of IL remarkably suppressed the increase in hydroxyproline content and abated the lung histological injury induced by BLM. There was a decrease in SOD activity and an increase in MDA level in lung tissue and serum in the BLM-Sal group (p < 0.01 , p < 0.01, vs. Sal-Sal group, respectively). And IL could obviously enhance the SOD activity and decrease the MDA level in a concentration-dependent manner. Moreover, IL also significantly inhibited the overexpression of TNF-alpha and TGF-beta (1) induced by BLM. These results indicated that IL possessed a significant inhibitory effect on BLM-induced pulmonary fibrosis, probably due to its antioxidant and/or anti-inflammatory activities and inhibitory overexpressing TNF-alpha and TGF-beta (1) induced by BLM.