Marine organisms seem to contribute remarkable drugs for several diseases. Many antimicrobial agents have been characterized from the marine organisms which defend against several opportunistic pathogenic infections. Antimicrobial peptides are a major component of the innate immune defence system in marine invertebrates. In such a way an antimicrobial peptide from the hemolymph of a marine crab Eurypanopeus orientalis was isolated for the first time and it seems to have an immense antimicrobial effect against the bacteria Salmonella typhii. A maximum antimicrobial effect of 17mm was recorded against these pathogens. The preliminary analytical screening of active crab hemolymph with thin layer chromatography assured the presence of peptides in it. The exact peptide which possesses the antimicrobial effect from the hemolymph was then isolated by purification through RP-HPLC. The active peptide fraction was then quantified using SDS PAGE analysis and 1H-NMR and ESI-MS studies for their determination of molecular weight. The antimicrobial peptide isolated was a 16 k Da peptide and its mass range was quantified to be 431 m/z range. Further the 3 dimensional structure prediction of the isolated antimicrobial peptide through X-ray crystallography is in progress for molecular docking studies. The present study indicates that the hemolymph of E.orientalis crabs may possess potential antibiotics.