Abstract: Objective To observe the ultrastructure of human amniotic mesenchymal stem cells( AMSCs) .Methods: human AMSC from full-term newborn amnion were isolated and cultured，and then subcultured，amplificated，and cell morphology was observed by microscopy．The Flow detection and identification of human AMSCs phenotype of at passage 3 were analyzed．Transmission and scanning electron microscopy were used to observe the ultrastructure of human AMSC．Results The appearance of human AMSC was spindle-shaped and polygonal．the hAMSC expressed immunophenotype CD44，CD90，CD105 and vimentin，did not express CD34，CD45．The short and thick microvilli processes were seen at the surface of human AMSC by scanning electron microscope． morpholigies of human AMSC were seen under transmissionelectron microscope，the cell was in a relatively active period in which a large and round or oval nucleus in the one cell were observed，The chromatin sparsely distributed in the nucleus，and cytoplasm was in much quantity．the organelles of mitochondria ，rough endoplasmic reticulum , golgi apparatus and small vesicle were rich．Conclusions Ultrastructure of Human Amniotic Mesenchymal Stem Cells has the biological characteristics of mesenchymal stem cells. the organelles of mitochondria ，rough endoplasmic reticulum and golgi apparatus were rich.Suggest it has a large number of secretory protein function, this is likely to be basis of cell paracrine function of amniotic mesenchymal stem cells.

Key words: Key words： mesenchymal stem cell, amoion, ultrastructure, human