Abstract: This study researched different molecular weight peptides on oral bio-availability. On the basis of smaller molecular weight with easier absorbed, three molecular weight peptides(<1 ku，1-3 ku，3-6 ku) were experimented on rat，then chose a collagen peptides with high oral bio-availability by determining the hydroxyproline content of feces, urine, and blood. The result showed that 1-3 ku cod skin collagen peptides exhibits higher oral bio-availability. This research would provide a base for health care production.

Key words: different molecular weight, peptide, hydroxyproline, oral bio-availability