The trophoblast is fetal-derived and in direct contact with maternal tissues. The expression of the various types of MHC antigen in trophoblast cells is very important for successful pregnancy. Among nonclassical MHC class Ⅰ antigens, HLA-G is expressed specifically on cytotrophoblast cells and its expression protects the fetal from maternal immune attack. The expression of the distinct subtypes of classical MHC class Ⅰ antigen is different in different subtypes of trophoblast cells. The expression of MHC class Ⅱ antigen is inhibited in trophoblast during pregnancy. It is suggested that C Ⅱ TA plays an important role in regulation of MHC class Ⅱ gene expression.