Abstract: The composite- modified nano- superparamagnetic Fe3O4 particle aggregates as the carrier,α- amylase was immobilized by method of covalent linkage. The application performance of immobilized α- amylase and free α- amylase were studied.The temperature,p H value,the operation stability and the basic kinetics of them were compared,respectively. The results showed that optimal p H value and temperature of immobilized α- amylase were 7 and 60 ℃,general similar with that of free α- amylase. Compared with the free α- amylase,immobilized α- amylase had better resistance of acid,alkali and temperature.After 10 recycles,relative activity of immobilized enzyme was still remaining 72.09%,half- life period deduced18.97 times.Immobilized α- amylase had better operation stability. Kmof immobilized α- amylase was 45.31 mg / m L,and the affinity was weaker than free α- amylase.