The present invention relates to novel common marmoset (Callithrix jacchus) embryonic stem cell cultures and cell lines, and their use. The common marmoset embryonic cells of the present invention (i) are capable of prolonged undifferentiated proliferation in vitro, (ii) maintain, during prolonged culture, a karyotype in which all the chromosomal characteristics of common marmoset are present without noticeable alteration; (iii) are capable of differentiation into all three embryonic germ layers (ectoderm, endoderm and mesoderm) even after prolonged culture; and (iv) are capable of teratoma formation in vivo. The stem cells preferably are totipotent.