Abstract: The effects of two lectins from Undaria pinnatifida and Scytosiphon lomentarius on the activities of acid phosphatase(ACP),alkaline phosphatase(AKP),lysozyme(LSZ)and catalase(CAT)of A.japonicus were studied by supplying various Undaria pinnatifida-lectin or S.lomentariuslectin levels in diets.The experimental dietary levels of U.pinnatifida lectin were 0.58%(m/m),1.16% and 2.32%,and those of S.lomentarius lectin were 0.32%,0.64% and 1.28%,respectively.Group fed with basic feed was set as control.On the 4th,8th,13th and 17th day after feeding,the activities of ACP,AKP,LSZ and CAT in A.japonicus were determined.The results indicated that the activity of ACP sustainably increased and was higher than the control among 17 days.The activities of LSZ increased firstly after lectins feeding except S.lomentarius lectin on 17th day,which decreased on this day,and the activities of LSZ were proportionally related to the additional dosage of two kinds of lectins.The CAT activity of U.pinnatifida lectin groups increased as the time went on,however CAT activity,firstly increased and then decreased in S.lomentarius lectin groups.