Abstract: The effect of different ultrasonic pretreatment time on the release of tuna skin-derived ACE inhibition peptides during enzymatic hydrolysis was investigated using hydrolysis degree and ACE inhibition rate by electrophoresis,HPLC,fourier transform infrared spectroscopy(FTIR)and differential scanning calorimetry(DSC). Results showed that the hydrolysis degree of the hydrolyzate in the ultrasonic pretreatment group was significantly different from that in the untreated group(p<0.05)after hydrolyzed for 5 min,and the ACE inhibition rate was higher than that of untreated group,indicating that the mode of tuna skin collagen hydrolysis was changed by ultrasonic pretreatment to promote the rapid release of collagen ACE inhibition peptides during short-term hydrolysis. Electrophoresis and HPLC results showed that the content of small molecular components below 10 kDa varied with the enzymatic hydrolysis process,which was accelerated by ultrasound pretreatment. FTIR and DSC showed that the internal hydrogen bonds and the triple helix structure of tuna skin collagen could be destroyed by ultrasound pretreatment,which was contributed to the expose of restriction site of triple-helix region and accelerated the release of ACE inhibition peptides during short-term hydrolysis.