To further study the functional characteristics of Apostichopus japonicus mannanbinding lectin(AJ-MBL)and to improve the natural immunity of A.japonicus, a prokaryotic vector of AJ-MBL gene CDS region was constructed.The fusion protein was expressed and purified in prokaryotic system and its bioactivity was studied.The coding sequence of AJ-MBL was amplified by RT-PCR method.After being identified by the restriction digestion and sequencing,the 498 bp of AJ-MBL gene was inserted into pET28a plasmid to yield an identified recombinant plasmid pET-AJ-MBL,which was used to transform the competent expressive cells of E.coli BL21(DE3).After induction with IPTG,samples analysis results revealed that a fusion protein of approximately 17 ku was yielded,and it occurred in the form of inclusion bodies,and could be purified with Ni²⁺ affinity chromatography.The results showed highly expressed fusion protein was acquired.The purified 17ku AJ-MBL underwent hemagglutination assay to test its bioactivity,the results showed that the minimum hemagglutination concentration was 10 μg/mL.These results indicated that the CDS domain of AJ-MBL had high expressed and the fusion protein(17 ku AJ-MBL)was highly bioactivity.