Abstract: To explore the method for isolation, culture and expandition of placentaderived mesenchymal stem cells(MSCs) in vitro. Methods： Mononuclear cells were harvested after placenta tissues were digested by collagenaseIV, and seeded in lowglucose DMEM containing 10%FBS, they were cultured and expanded in vitro, their markers were detected by flow cytometry; cells of 3 passages were induced to differentiate into osteoblast with vitamin C dexamethasone and βglycerophoshate disodium saltpentahydrate, induced cells were observed the change of alkaline phpsphatase activity and matrix mineralization. Results： B day 714 some adherent cells were observed and expanded same as spindle cells ,the result showed that adherent cells were positive for CD29，　CD44 and CD105,　but negative for CD34，　CD45，　CD19;　under the induced condition histological analysis of the cells revealed strong with alkaline phosphatase method and alizarin red confirmed that the cells had osteogenic potential. Conclusion： Placental mesenchymal stem cells could be regarded as an alternative source of MSCs.

Key words: Placenta, Mesenchymal stem cells, Differentiation, Osteoblasts