Abstract: The effects of three lectins fromUndaria pinnatifida lectin,Ulva pertusa  lectin andScytosiphon lomentarius lectin on the activities of Superoxide dismutase (SOD), Polyphenol oxidase (PO) ofApostichopus japonicus were studied by supplying various lectin . The experimental dietary levels ofUndaria pinnatifida lectin were 0.90%(m/m), 1.80% and 3.60%, andUlvapertusa lectin were 1.36%、2.73%、5.45%, andScytosiphon lomentarius lectin were 0.47%、0.94%、1.88% respectively, Group fed with basic feed was set as control. On the 5th, 10th, 15th and 20th day after feeding, the activities of Superoxide dismutase (SOD) and Polyphenol oxidase (PO) inApostichopus japonicus were determined.The results indicated that the activities of SOD and PO of each group increased,respectively, has a significant difference(P <0.05) and a highly significant difference (P <0.01), with the control group. Feeding 1.80% concentration group ofUndaria pinnatifida lectin；1.36% concentration group ofUlva pertusa lectin；1.88% concentration group ofScytosiphon lomentarius lectin are best. The results show that marine algae lectin can be used as theApostichopus japonicus immune enhancer, it is recommended that the appropriate dosage: 1.80%Undaria pinnatifida lectin, 1.36%Ulva pertusa lectin and 1.88%Scytosiphon lomentarius lectin