Abstract: Aim To prepare and characterize the monoclonal antibody against poly-mannaguluronic acid (911). Methods A hybridoma cell line was obtained by cloning for 3 times those cells that secret antibody against 911 after the fusion of NS-1 myelome cells with spleen cells from Balb/c mice immunized with a 911-bovine serum albumin conjugate, prepared by reductive amination. Hybridoma was inoculated to Balb/c mouse to induce ascites. The antibody was purified by ammonium sulfate and Protein A - Sepharose CL-4B. DD3 was confirmed to be fusion cells after determination of DNA content with flow cytometry. Competitive inhibitory test and Biacore confirmed the cross-reactivity of the antibody with other endogenous polysaccharides or with alginic acid sodium. Igs′ classes and subclasses were identified by Isostrip^TM method. The affinity of DD3 was verified by ELISA. Results A hybridoma cell line secreting monoclonal antibody against 911 (marine sulfate polysaccharide) named DD3 was obtained. The DD3 ascites contained specific antibody with titer over 1.0×10₅. There was no cross-reactivity of these antibodies with other endogenous polysaccharides or with alginic acid sodium. The immunoglobulin subclass of DD3 was IgG2a, κ type. The affinity of DD3 was 2.0×10₈ L·mol^-1. Conclusion One hybirdoma line (DD3) secreting monoclonal antibody against 911 was established to provide a potential method for the pharmacokinetic study of 911.