Previously, we have shown that Atlantic mackerel represents a valuable source of food with high nutritional value l16]. Mackerel hydrolysate using protamex was shown to contain high amounts of proteins and well-balanced fat and amino acid composition[16 Recently, we isolated antibacterial peptide fractions in mackerel processing by-products hydrolysed using commercial enzymes(protamex, papain, neutrase, and flavourzyme) [17l. These active fractions had low molecular weights and were active against Gram positive(Listeria innocua) and Gram-negative(Escherichia coli) bacteria. The objective of the present study was to identify and to characterize AMPs from mackerel by-products hydrolysed using protamex