Differentiation-promoting agent of ES cells containing the uPA, the present invention relates to a prophylactic agent of teratoma or differentiation-promoting agent of ES cells into hepatocytes preferably. Furthermore, the differentiation method of promoting ES cells which comprises contacting the ES cells uPA, is brought into contact with the ES cells uPA or promoting differentiation method, of ES cells into hepatocytes, the present invention, the liver and the ES cells, preferably a process for the preparation of liver cells comprising allowing the cells to differentiate.本発明は、uPAを含有するES細胞の分化促進剤、好ましくはES細胞から肝細胞への分化促進剤またはテラトーマの予防剤に関する。また、本発明は、uPAをES細胞に接触させることを含むES細胞の分化促進方法、好ましくはES細胞から肝細胞への分化促進方法、またはuPAをES細胞に接触させ、当該ES細胞を肝細胞に分化させることを含む肝細胞の調製方法に関する。
