This study was purposed to compare the biological characteristics of umbilical cord-derived mesenchymal stem cells (UC-MSCs) and bone marrow-derived mesenchymal stem cells (BM-MSCs). The frequency of successful isolation, cell yield, colony-forming units-fibroblastics (CFU-F), proliferation capacity, immunophenotype and multi-differentiation potentials of UC-MSCs and BM-MSCs were determined by limiting dilution assay, flow cytometry, invert microscopy, RT-PCR and so on, the determined results were compared. The results showed that MSCs were successfully isolated from all the 36 portion of UC tissue and 8 portion of BM. Although the mean number of nucleated cells isolated from UC tissue was significantly lower than that from BMs (1 x 10(6)/cm vs 5.5 x 10(7)/ml) (p=0.0002), no significant differences of the yield of adherent cells were observed (8.6 x 10(5)/cm vs 8.4 x 10(5)/ml) (p>0.05). UC-MSCs shared the most of the characteristic of BM-MSC, including fibroblastic-like morphology, typical immunophenotype, cell cycle status, adipogenic and osteogenic differentiation potentials. However, the CFU-F frequency was higher in UC (1:1609+/-0.18) than that in BM (1:35700+/-0.01) (p<0.05). Furthermore, the proliferation capacity of UC-MSCs was higher than that of BM-MSCs; the expressions of CD106 and HLA-class I in UC-MSCs were lower than those in BM-MSCs (p<0.05). It is concluded that the cell yield and most biological characteristics of UC-MSCs are similar to BM-MSCs, but UC-MSCs possess the higher proliferation capacity, and the lower expression of HLA-class I and HLA-DR as compared with BM-MSCs, therefore the human umbilical cord tissue may be considered as a promising alternative to bone marrow as a source of MSCs.