In order to explore the cytotoxic potential of sponge associated marine bacteria, bacterial colonies were obtained from marine sponge Spirastrella inconstans. Totally 14 aerobic, heterotropic and morphologically different bacterial strains were purified and cultured in marine broth. Crude metabolite was extracted using ethylacetate as extracting solvent. The metabolites were tested for its antiproliferative activity against A549 lung adenocarcinoma cell line. The colorimetric based MTT assay revealed strain MB13 as potent cytotoxic bacterium. The strain was identified as Pseudoalteromonas piscicida using 16s rRNA sequencing and biochemical test.