Neutral proteinase was covalently attached to amine-terminaled magnetic particles and cross-linking it with glutaraldehyde. Activity of MIE arrive 45 000 U/g (magnetic particles). Optimum conditions of immobilization were studied. Stabilities to heat and preservation,operational stability of free enzyme and MIE also were compared. Some properties of MIE, such as optimum pH is 7.5, optimum temperature is 60℃ were confirmed.