MMTV induces the mouse mammary tumor through the dysregulation of Notch, Wnt, or Fgf signaling pathway. Activation of Notch signaling pathway leads to transcriptional activation of Hes family genes through the interaction between Notch intracellular domain and RBPSUH (CSL). Hes family proteins are mammalian homologs of Drosophila Hairy and Enhancer of split. Hes family of transcriptional repressors with basic Helix-loop-helix (bHLH) and Orange domains are implicated in the cell fate determination of stem cells (or precursor cells) by suppressing the expression of tissue-specific transcriptional activators. Human HES1, HES4, HES6, and HES7 genes have been reported by other groups. Here, we identified and characterized human HES2, HES3 and HES5 genes by using bioinformatics. FLJ33803 (AK091122.1) was the representative human HES2 cDNA. HES2 gene, encoding a 173-aa protein, was located within human genome sequence AL031848.11. HES3 gene, encoding a 186-aa protein, was identified within human genome sequence AL031847.17. HES5 gene, encoding a 166-aa protein, was identified within human genome sequence AL139246.20. HES2 and HES3 genes were mapped to human chromosome 1p36.31, while HES5 gene to 1p36.32. HES2 mRNA was expressed in placenta, pancreatic cancer, colon cancer with RER, cervical cancer, and in head and neck tumors. HES5 mRNA was expressed in fetal heart, and brain tumors. Human HES family proteins were found consisting of bHLH, Orange, Proline-rich domains, and WRPW motif. Phylogenetic analyses revealed that HES family proteins were distantly related except a paralog pair of HES1 and HES4. HES family genes are pharmacogenomic targets in the field of regenerative medicine and oncology.