S-8300,a small (8200.901 Da) antidiabetic peptide,was isolated from shark livers (Chiloscyllium plagiosum) through extraction of the water-soluble fraction,dialysis,ultrafiltration and DEAE-Sephorose,Bio-Gel P-10 and FPLC monoQ chromatography.It was stable at 95℃ for 30min and stable between pH3.0 to 9.0.It was not inactivated by DNase and RNase,but totally inactivated by trypsin and proteinase K digestion.In addition,S-8300 could remarkably protect the structure integrity and recover the damage of NIT-1 cell after exposed to the toxin of STZ.The result of N-terminal amino acid sequence was NH2-Met-Len-Val-Gly-Pro-Ile-Gly-Ala-Ala-Lys-analyzed by Edman method,which revealed that the N-terminal sequence (residues from 1 to 10)of the peptide was totally new.