Normal tissue damage following radiotherapy (RT) represents a major problem in cancer treatment. Among the common side effects of RT are the structural and functional alterations in the oral mucosa as well as in the salivary glands, since these structures are inevitably exposed to ionizing radiation during head and neck RT. These effects are demonstrated by the development of oral mucositis and xerostomia which greatly interfere with RT. In spite of the fact that several agents developed over many years in order to prevent &/or treat these conditions, yet, an agent that is completely successful doesn't exist as most agents aim at palliative treatment rather than actual prevention.Currently, stem cell research has received great attention especially in the field of regenerative medicine. Hence, based on the major advances made in this field, stem cell-based therapy may play a great role in preventing &/or treating normal tissue damage following RT. So, the current work aimed at exploring the possible role of bone marrow mesenchymal stem cells in ameliorating the side effects of ionizing radiation on the tongue structure via histological & immunohistochemical examination.