Stem cells are undifferentiated cells characterized by self renewal,multipotency, long term tissue repopulation after transplantation , serial transplant ability and when divide the daughter cell can either fully differentiated or remain stem cell. Haematopoietic stem cells can be differentiated into hepatocytes, cardiomyocytes, brain cells, hair follicles and sebaceous glands, epithelial and nonepithelial cell types in the kidney, islet cells in pancreas, type II pneumocytes in the lungs, mucous secreting cells in the stomach, goblet cells and enteroendocrine cells in the intestine. For treatment of genetic diseases, transplantation of genetically modified autologous marrow would avoid many of the risksof allogenic transplants. It is used in treatment of many diseases as cystic fibrosis, Duchenne muscular dystrophy, immunodeficiency diseases, some types of anemias like thalassemia and sickle cell anemia and in wound healing, gastero-intestinal diseases and autoimmune diseases.Recent new insights into stem cell biology have changed ourunderstanding of regenerative activities in the infarcted heart and have raised considerable hopes for novel therapeutic approaches aimed at cardiomyocyte replacement/regeneration through cell transplantation ("cellular cardiomyoplasty").