Abstract: Casomorphin is a group of structurally similar small peptides produced by enzyme degradation of β-casein. It has the function similar to opioid. To develop a HPLC method for assaying similar peptides. A acetonitrile-H2O (3:1) was used as mobile phase and 0.1% phosphate acid used as acidic modifier. Gradient elution was adopted with Kromasil C8 column (5μm, 4.6mm×200mm) with ultraviolet detector at 215nm. The retention of β-casomorphin-7 andβ-casomorphin-5 were 21.45min and 11.474 min respectively .And a good linear relationship exited between peak area and casomorphin concentrations ranged from 0.125～1.0mg/ml(r=0.9989). The RSD of purity and migration time of β-casomorphin-7 and β-casomorphin-5 were 7.29% and 5.19% respectively. This method provided a simple and feasible way to analyze casomorphins especially those similar peptides.

Key words: HPLC, casomorphin, peptide