Abstract: Marine animals have great potential for providing novel drug leads with novel mechanism of action. The aim of the present study was to evaluate the antimicrobial potency of methanolic extract of whole body tissue of Sepiella inermis and Ethylene Diamine Tetra Acetate (EDTA) extract of cuttlebone (polysaccharides) against ten human pathogens. S. inermis tissue was extracted with 100% methanol for about 48 h, centrifuged and supernatant was concentrated under vacuum in desiccator. The polysaccharide extract was obtained from the internal shell using 10 mM hot EDTA. The final product was used for assaying the antibacterial activity by disc diffusion method in different concentrations. In 100% concentration, the highest inhibition zone of 12 mm was observed against Klebsiella pneumoniae and Staphylococcus aureus in methanolic extract of whole body tissue and Staphylococcus aureus alone in EDTA extract from cuttlebone. In 75% concentration, methanolic extract showed highest activity of 9 mm against K. pneumoniae, Staphylococcus aureus and Staphylococcus pneumoniae whereas the EDTA extract showed highest activity 8 mm against Vibrio cholerae, Klebsiella pneumoniae and Vibrio alginolyticus. In 50% concentration, the maximum activity of 9 mm was recorded against Klebsiella pneumoniae and Staphylococcus aureus in methanolic extract; whereas maximum activity (11 mm) was recorded against E. coli in EDTA extract. In 25% concentration, the both maximum and minimum activity 7 mm was recorded against Pseudomonas aeruginosa, Klebsiella pneumoniae, Staphylococcus aureus and Streptococcus aureus in methanolic extract; Vibrio alginolyticus in EDTA extract. This study reveals that both the methanolic extract of the whole body tissue and EDTA extract of cuttlebone have good antimicrobial activity depending on the concentration.