Abstract: Both induced and non-induced hemolymphs were collected from the mud-crab, Scylla serrata and were subjected to antibacterial assay to investigate the presence of inducible and constitutive antibacterial protein(s). Induction was done by injecting Escherichia coli ATCC 25922. The induced hemolymph showed antibacterial activity against a range of different strains of marine or non-marine gram-positive and gram-negative bacteria including few antibiotic resistant strains, whereas the non-induced hemolymph was not appeared to be active against those tested. The induced hemolymph was subjected to SDS-PAGE and seven proteins were detected. The molecular weight of which were in the range from 36 to 84.5 kDa. The hemolymph proteins were fractionated by gel filtration chromatography. Repeated antibacterial assay of the chromatographic fractions against previously proved hemolymph sensitive bacteria showed that only a few fractions were responsible for the activity and that the fraction purified proteins showed better activity than the crude hemolymph. Total five different proteins were present in all the fractions detected by SDS-PAGE analysis. The molecular weights were 64 kDa, 61 kDa, 56.5 kDa, 49 kDa and 36 kDa.