Cells in the pluripotent ground state can give rise to somatic cells and germ cells, and the acquisition of pluripotency is dependent on the expression of Nanog. Pluripotency is conserved in the primitive ectoderm of embryos from mammals and urodele amphibians, and here we report the isolation of a Nanog ortholog from axolotls (axNanog). axNanog does not contain a tryptophan repeat domain and is expressed as a monomer in the axolotl animal cap. The monomeric form is sufficient to regulate pluripotency in mouse embryonic stem cells, but axNanog dimers are required to rescue LIF-independent self-renewal. Our results show that protein interactions mediated by Nanog dimerization promote proliferation. More importantly, they demonstrate that the mechanisms governing pluripotency are conserved from urodele amphibians to mammals.