Abstract: Using the monoclonal antibodies(Mab)3F4 against granulocyte of swimming crab(Portunus trituberculatus)to research the cross reaction of other seven species of crustaceans(Penaeus vannamei,Fenneropenaeus chinensis,Metapenaeus ensis,Oratosquilla oratoria,Eriocheir sinensis,Petalomera japonica,Cancer magister).In this paper,laser scanning confocal microscopy(LSCM),Western blot and Flow Cytometry(FCM)were employed to detect the relationship between these seven species.Balb/C mice were immunized by heamocytes of Portunus trituberculatus.Spleens were dissected from the immunized Balb/c mice and the cells were fused with SP2/0 myeloma cell line using polyethylene glycol as fusogen.Hybridomaculture mediums of hybridoma cells were selected using Indirect Immunofluorescence Assay(IFA)screening methods.One positive hybridoma was found which secreted high titer antibody,followed by single-cell cloning and subcloning by limiting dilution method and tested again for their specificity by IFA at the appropriate stage of growth.Single-cell cloning was repeated at least twice so as to prove the monoclonality of the hybridoma culture supernatant.We got the MAb 3F4 specific against granulocyte of swimming crab(Portunus trituberculatus).MAb 3F4 showed strong immunofluorescent reaction with granulocytes,but no reaction with hyalinocytes.In cross-reactivity,LSCM showed the MAb 3F4 could also react with haemocytes of Eriocheir sinensis and Petalomera japonica. Sorted by FCM,MAb 3F4 was positive to the two types of heamocytes of Eriocheir sinensis(hyalinocyte and granulocyte),and the percentage of positive rate were 57.72% and 77.05% respectively.Reacting with haemocyte of Petalomera japonica was mainly positive to granulocyte,whose positive rate was 82.59%,but that to the hyalinocyte was only 9.57%.Analyzed by Western blot,MAb 3F4 was recognized as one heamocyte protein of Eriocheir sinensis,whose molecule weight was 30 ku,but there was no protein band on nitrocellulose membrane of Petalomera japonica.