Lectin plays an important role in nonspecific immunity of invertebrates by including bacterial agglutination, nonselfrecognition, as opsonin and enhancing cell phagocytosis. In this paper, the author reported the purification and monoclonal antibodies (mAbs) preparation of lectin from mud crab, Scylla serrata, as well as the application of mAbs for lectin location by indirect immunofluorescence. Lectin was isolated from hemolymph of mud crab by affinity chromatography using Sepharose 4B coupled with NAcetylDglucosamine (GlcNac) which could specifically bind to mud crab lectin. The serum of S. serrata was applied to the column and the lectin binding to the column could be eluted by 0.45 mol/L NaCl TrisHCl buffer with a single peak. The agglutinating specific activity of elution peak was equated 32.6 times of original serum, and SDSPAGE showed the two main components of lectin with 87 ku and 79 ku. Seven hybridoma cell lines named BF82 etc., secreting antibodies against mud crab lectin, were prepared by hybridoma technique. Ascitic fluids of mAbs were 1∶10⁴-1∶10⁵ titers of indirectELISA by coated purified lectin. The mAbs could inhibit the hemagglutination of mud crab lectin with 1∶32-1∶64 titers. The Ig isotype for all seven mAbs were IgG1.The Western blots displayed that the mAbs specifically binded to the bands of 87 ku and 79 ku. Haemocytes of S. serrata were used for location of lectin by using indirect immunofluorescence technology; the results suggested that lectin is mainly distributed in the granules of granule hemocyte and the membrane of hyaline hemocyte.