Background:Mesenchymal stem cells (MSCs) represent a promising tool for the regeneration of damaged tissues in clinical applications because they are characterized as undifferentiated cells, able to self-renew with a high proliferative capacity, and possess a mesodermal differentiation potential.Bone marrow (BM) was the first source reported to contain MSCs. However, for clinical use, BM may be detrimental due to the highly invasive donation procedure. More recently, umbilical cord blood (UCB), attainable by a less invasive method, was introduced as an alternative source for MSCs. Another promising source is adipose tissue (AT). Aim of the Work: The aim of this study is to investigate the possibility of obtaining culture expanded MSCs from UCB and AT and also to know whether MSCs derived from both sources share the same characteristics with respect to their expansion characteristics and cell surface antigen expression. Material and Methods: UCB and AT were collected and the isolated mononuclear cells were cultured, the adherent MSCs were then expanded with transferring into passages by trypsinization after (90 – 95%) confluency until senescence, MSCs surface markers expression was evaluated after the 3rd and 5th passages by flowcytometry. five surface antigens were tested CD90, CD105, CD44, CD45 and CD34. Results: Differences were observed concerning doubling rate of cells and also the lag period between passages. UCB derived MSCs showed higher doubling rate (17.25) with shorter lag period (2 – 3 days) compared to a lower doubling rate (3.9) and longer lag period (6 – 7 days) for AT derived MSCs. UCB derived MSCs continued in culture without senescence until the 12th passage while AT derived MSCs ceased proliferation and showed senescence at the 6th passage.No significant differences concerning the immune phenotype of the MSCs derived from both UCB and AT as all cells were uniformly positive for: Endolgin Receptor (CD 105), Extracellular matrix protein (CD90), Hyaluronate receptor (CD44). Cells were also negative for: Leukocyte common antigen (CD45) and Hematopoietic progenitor cell marker (CD34).Conclusion:Our data showed that both UCB and AT are an alternative less invasive attainable sources for MSCs rather than Bone Marrow, also UCB-MSCs showed higher expansion potential and doubling rate with delayed senescence than AT-MSCs.