SOX2 and POU5F1 (OCT3 or OCT4) transcription factors are implicated in FGF4 expression in embryonic stem (ES) cells. SOX2, POU5F1, and FGF4 are key molecules for the integrome network in oncology and stem cell biology. SOX2 gene at human chromosome 3q26.33, SOX1 gene at 13q34, and SOX3 gene at Xq27.1 constitute a subfamily among the SOX gene family. Here, rat Sox2 and Xenopus sox2 genes were identified and characterized by using bioinformatics for comparative genomics and comparative proteomics analyses. Rat Sox2 gene, encoding a 319-aa protein, was located around the nucleotide position 73213-75621 of rat genome sequence AC123231.4. Xenopus tropicalis sox2 complete coding sequence, encoding a 311-aa protein, was derived from CR760314.1 cDNA. Rat Sox2 showed 98.4%, 97.8%, 92.2%, 88.1% and 86.8% total amino-acid identity with mouse Sox2, human SOX2, chicken sox2, Xenopus sox2 and zebrafish sox2, respectively. SOX123C domain was identified as the novel domain corresponding to the C-terminal region conserved among SOX1, SOX2 and SOX3 orthologs. Vertebrate SOX1, SOX2 and SOX3 orthologs were found consisting of HMG box and SOX123C domain. SOX9, TCF/LEF, POU2F1 and COMP1 binding sites were conserved among human SOX2 promoter, rat Sox2 promoter, and mouse Sox2 promoter. SOX2 mRNA was expressed in ES cells, fetal brain, anaplastic oligodendroglioma, rhabdomyosarcoma, and small cell lung carcinoma. Due to the pivotal role of SOX2 in the early embryogenesis, SOX2 promoter and SOX2 protein were well conserved during vertebrate evolution. This is the first report on comparative integromics analyses on the SOX2 orthologs.