Liver damage, including hepatitis, that is induced by chemicals or viruses often leads to liver fibrosis and sometimes leads to subsequent liver cirrhosis. For severe liver-associated diseases such as cirrhosis, liver transplantation is one of the most effective treatments. However, due to the shortage in donated organs and the growing list of patients in need of such intervention, transplantation is often not common.Stem cells and their possible use in cell therapy have drawn much attention recently, due to their potential for self-renewal and differentiation. Mesenchymal stem cells in vitro have the potential to differentiate into hepatocytes.The aim of this work was to isolate and in vitro characterize the mesenchymal stem cells obtained from rat bone marrow and adipose tissue. Also, the study was extended to test in vivo, the hypothesis of treatment of liver fibrosis by transplanting bone marrow or adipose tissue derived mesenchymal cells in rats model.