The present invention provides a preparation method of a chimeric embryo and a chimeric rat, which is characterized by contacting a rat pluripotent stem cell and a host embryo in the presence of an ES cell differentiation inhibitor. The method includes (a) a step for contacting a fertilized host embryo collected from a female rat and a rat pluripotent stem cell in the presence of an ES cell differentiation suppressant, and (b) a step for culturing the host embryo in contact with the rat pluripotent stem cell to form a chimeric embryo.
