This protocol describes a method to graft conventional primed pluripotent stem cells (PSCs) and region-selective PSCs to different locations of post-implantation mouse epiblast followed by in vitro embryo culture. Compared to conventionally used teratoma formation assay, epiblast grafting offers a more relevant in vivo test for evaluating the primed PSCs’ pluripotency and uniquely serves to distinguish different flavors of primed PSCs that harbor distinct spatial properties. Moreover, the observation that grafted human rsESCs could enter into early mouse embryogenesis provides a novel way of studying human development.