Abstract: The purpose of this study was to develop a new enzyme for industrial production.A kind of marine coldadapted α- amylase was adopted to hydrolyze corn starch. Some factors which could influence enzymatic hydrolysis were studied.The optimal conditions of corn starch hydrolysis with the α- amylase: temperature 30 ℃,hydrolysis time 90 min,substrate concentration 4.5%,enzyme amount 8 U / g and p H6.5. The amylase could hydrolyze raw starch into maltose,maltotriose,isomaltotriose,maltotetraose and maltopentaose by TLC and HPLC of analysis. The quantity of maltotetraose and maltopentaose was 69.62%. The hydrolyzate had the scavenging effect on the hydroxyl radical and DPPH radical.The scavenging effect of the hydroxyl radical was better than the DPPH radical.