Objective To investigate the expression of surface antigen of human periodontal ligament cells （PDLCs） and dental pulp cells（DPCs） and the impact of ex vivo expansion to the expression of surface antigen. To provide basis of proper surface antigen for further selection of homogenous stem cell subpopulation from PDLCs and PCs. Methods PDLCs and DPCs were isolated and cultured by collagenase type I and dispase. The expression of surface antigen was analyzed by immunohistochemistry and flow cytometry. Results Positive expression of STRO-1 and CD146 were observed in PDLCs and DPCs by immunocytochemistry. Similar to DPCs, PDLCs expressed mesenchymal stem cell markers STRO-1, CD146, CD29, CD44 and CD106, and displayed negative expression for CD34 at passage 1 by flow cytometry. There were no significant difference of STRO-1, CD29 and CD44 expression level between PDLCs and DPCs（P>0.05）. PDLCs expressed significantly higher level of CD106 and significantly lower level of CD146 than DPCs（P
