The possible protective effect of Losartan, an angiotensin II receptor 1 antagonist, on bleomycininduced rat lung fibrosis was evaluated using histological and immunohistochemical techniques. Twenty adult male albino rats were divided into 4 groups each of five rats: Group I (control) given saline both I.V and orally, Group II given bleomycin 10mg/Kg/day I.V., Group III given losartan 10 mg/Kg/day orally and Group IV given both bleomycin and losartan. Lung sections were taken at the 28th day of the experiment, stained with H&E, Masson's trichrome, Orcein and immunohistochemical stain for α-SMA. This was followed by morphometric measurements and statistical analysis. The present study showed that bleomycin induced fibrotic changes in the lung in the form of thickened interalveolar septa filled with proliferated type II pneumocytes, fibroblasts and inflammatory cells with significant increase in collagen and elastic fibres deposition and in α-SMA immunoreactivity. It was found that concomitant treatment with losartan (Group IV) showed significant reduction in these fibrotic changes. The changes in α-SMA immunoreactivity in different groups showed the same pattern as those of collagen and elastic fibres. Thus, it could be concluded that myofibroblasts might play a pivotal role in induction of lung fibrosis and they could be a target of future therapeutic strategies