Background: Silver nanoparticles (Ag-NPs) arenanomaterials that become used widely in severalapplications and products. Objective: The current work aimed at studying the Ag-NPs effects on the lung tissues ofadult male albino rats and to evaluate the potential ameliorating role of human umbilical cord mesenchymal stemcells (HUCMSCs) through biochemical, histopathological, immunohistochemical and ultra-structural lung tissuesexaminations. Material and methods: thirty adult male albino rats were divided into control groups (I), Ag-NPsgroup (II), received (300mg/kg) of Ag-NPs orally by gavage and Ag-NPs+ HUCMSCs (III), received Ag-NPs asgroup II and (0.5 × 106)/80 μl PBS of HUCMSCs by intravenous injection in rat tail vein for the two successive daysafter 4 weeks of AG-NPs administration. Lung tissues samples were examined for Nitric oxide (NO),Myeloperoxidase (MPO) activities and reduced glutathione (GSH) content. Moreover, the histopathological, ultrastructuraland immunohistochemical examinations were performed. Results: Ag-NPs induced oxidative stress byincreased NO, MPO activities, inducible nitric oxide synthase (iNOS) expressing cells and decreased GSH contentsin lung tissues. In additionally, Ag-NPs caused histopathological and ultra-structural alterations. HUCMSCs restored most of histological and ultra-structural architecture. Furthermore, reduced NO, MPO activities, iNOS expressing cells and increased GSH contents of lung tissues. Conclusion: HUCMSCs have a potential promising role inimproving oxidative stress caused lung injury induced by Ag-NPs in adult male rats.