Background: Pulmonary fibrosis (PF) is a chronic fibrotic lung disease. Lung parenchyma and architecture is destroyed, compliance is lost, and gas exchange is compromised in this debilitating condition that leads to respiratory failure. NAC is a precursor of L-cysteine that results in glutathione elevation biosynthesis. It acts directly as a scavenger of free radicals, especially oxygen radicals. This study aimed to evaluate the possible therapeutic effect of Adipose derived mesenchymal stem cells and N-acetylcysteine (NAC) on induced lung fibrosis in adult male albino rats. Methods: Ten rats were used to isolated adipose-derived stem cells and sixty rats were randomly divided into five groups. Group I (control group: 20 rats), Group II (affected group:10 rats), Group III (Adipose stem cell group: 10 rats), Group Iv (N-acetylcystiene group:10 rats) and Group v (Adipose stem cell + NAC group: 10 rats). Specimens taken and histological studies, immunohistochemical and morphometric study were performed. Results: Group II showed markedly thickened inter-alveolar septa and destruction with extensive cellular infiltrations, increases in macrophage and alveoli were Collapsed.And there is massive lymphocytic infiltration around bronchiolar wall.There was a significant decrease (P0.01) in Ki67 expression in group III, IV & V compared to group I. Conclusion: Each of NAC and adipose tissue-derived stem cells can protect against lung fibrosis caused by Bleomycin when administered prior to, and concomitant with bleomycin, but their combined administration have better results.