Abstract: Evaluating of antimicrobial activity of marine sponge extracts was carried out on the in vitro testing. Both the test on agar plates and broth microdilution method showed that Petrosia sp. is better at anti-microorganisms than the sponge Xestospongia testudinaria does. In fact, the total ethanol extract and the aqueous extract (the alcohol remaining after fractional separation of organic solvents) of Petrosia sponge showed significant antibacterial results against both Gram-negative and Gram-positive bacteria. These extracts inhibited Gram- negative bacteria Escherichia coli ATCC 13709 (MIC = 16 µg/mL, IC 50 ˂ 10.00 µg/mL) and Pseudomonas aeruginosa ATCC 15442 (MIC = 64 µg/mL, IC 50 ˂ 36 µg/mL), moreover killing Staphylococus aureus ATCC 13709, Bacillus subtilis ATCC 6633 and Lactobacillus fermentum N4 with IC 50 from 11.08 to 43.00 µg/mL. The remarkable result of this careful study is that the polar extracts of the Petrosia sp. inhibit bacteria more strongly than the organic extracts.