We aimed to investigate the preventive and treatment effect of molsidomine (MOL) on bleomycin (BLC)-induced lung injury in rats. Rats were assigned into groups as follows: control group; MOL group, 10 mg/kg MOL was continued orally for 29 day; BLC group, a single intratracheal injection of BLC (2.5 mg/kg), MOL+BLC-preventive group, 10 mg/kg MOL was administered 1 day before the intratracheal BLC injection and continued for 14 days; BLC+MOL-treatment group 10 mg/kg MOL was given on 14th day after the intratracheal BLC injection and continued until sacrifice. All animals were sacrificed on 29th day after BLC administration. The semiquantitative histopathological assessment, tissue levels of malondialdehyde (MDA), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), reduced glutathione (GSH), total antioxidant status (TAS), total oxidant status (TOS), myeloperoxidase (MPO), and oxidative stress index (OSI) were measured. BLC-provoked histological changes were significantly detected compared to the control group. MOL restored these histological damages in different quantity in the treatment and preventive groups. BLC administration significantly decreased levels of GSH and TAS when compared to controls and these reductions was significantly ameliorated by MOL given prophylactic setting. However, therapeutic MOL administration significantly increased the TAS level decreased by BLC. The levels of MDA, MPO, and TOS were significantly increased with BLM, and these augmentations of MDA and TOS were significantly reduced by MOL given prophylactic setting. Furthermore, the OSI was higher in the BLC group, and this increase was reversed by the MOL administration before and after BLC treatment. In this study, both protective and therapeutic effects of MOL against BLC-induced lung fibrosis were demonstrated for the first time.