SUMMARY Extraembryonic endoderm stem (XEN) cell lines can be derived and maintained in vitro and reflect the primitive endoderm cell lineage. SOX17 is thought to be required for the derivation and maintenance of mouse XEN cell lines. Here we have re-evaluated this requirement for SOX17. We derived multiple SOX17-deficient XEN cell lines from preimplantation embryos of a SOX17-Cre knockout strain and chemically converted multiple SOX17-deficient embryonic stem cell lines into XEN cell lines by transient culturing with retinoic acid and Activin A. We confirmed the XEN profile of SOX17-deficient cell lines by immunofluorescence with various markers, by NanoString gene expression analyses, and by their contribution to the extraembryonic endoderm of chimeric embryos produced by injecting these cells into blastocysts. Thus, SOX17 is not required for the derivation and maintenance of XEN cell lines.