While collagen was previously thought to be related to the moisture of skin, the correlation between orally ingested collagen and the moisture of skin had not been clarified. Based on recent studies regarding collagen peptide's ability to assist hyaluronan synthesis and to change the moisture content of the stratum corneum after oral ingestion of fish/porcine collagen, the relationship between the di-peptide in fish/porcine collagen, Proline-Proline/hydroxy-Prorine (Pro-Pro/HyP), and the moisture content of the stratum corneum was evaluated in this study. Moreover, collagen proteins in Eukaryotic genomes which are thought to be able to effectively increase the moisture content of the stratum corneum were retrieved from the UniProtKB/Swiss-Prot protein sequence database. Fish/porcine collagens which have high Pro-Pro/HyP frequency were components of filaments in spines, cartilage, ligament and bone. In addition, human and mouse organs with frequent elastic actions, including the kidney, lung, heart, muscles and skin, Pro-Pro/HyP-rich collagen proteins were found by comprehensive database scanning.