Background: Silver nanoparticles (Ag-NPs) arenanomaterials that become used widely in several applications and products. Objective: The current work aimed at studying the Ag-NPs effects on the lung tissues of adult male albino rats and to evaluate the potential ameliorating role of human umbilical cord mesenchymal stem cells (HUCMSCs) through biochemical, histopathological, immunhistochemical and ultra-structural lung tissues examinations. Material and methods: thirty adult male albino rats were divided into control groups (I), Ag-NPs group (II), received (300mg/kg) of Ag-NPs orally by gavage and Ag-NPs+ HUCMSCs (III), received Ag-NPs as group II and (0.5 × 106)/80 μl PBS of HUCMSCs by intravenous injection in rat tail vein for the two successive days after 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, ultra-structural and immunehistochemical examinations were performed. Results: Ag-NPs induced oxidative stress by increased NO, MPO activities, inducible nitric oxide synthase (iNOS) expressing cells and decreased GSH contents in 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 in improving oxidative stress caused lung injury induced by Ag-NPs in adult male rats.