<![CDATA[Phyllidiella nigra is an organism that is suspected to have secondary metabolites because their ability to develop its self defense system by camouflage and using chemical compounds derived from their nature diet as deterrent against their predators. The purpose of this study was to isolate symbiotic bacterial derived from P. nigra, extracted and followed by, the antibacterial assays against Escherichia coli and Bacillus megaterium as well as the anti-UV assay. The results showed that the five isolates tested had an antibacterial activity with the highest average inhibition zone against E. coli DSM 498 bacteria, isolate 1 (14.67 mm), isolate 5 (14 mm), and against B. Megaterium DSM 32T bacteria, isolate 3 (13.33 mm). The three isolates which had the highest inhibition zone and P. nigra extract were tested for anti-UV assay using a UV-Vis Spectrophotometer. The results obtained isolate 3 has absorption of UV-A with the UV absorbtion maximum at λ 340 nm and P. nigra extract has absorption on UV-B radiation with UV absorption maximum at λ 290 nm. Key words: Nudibranchia, Bacteria, Anti-bacteial, Anti-UV Phyllidiella nigra merupakan organisme yang diduga memiliki metabolit sekunder karena mampu mengembangkan sistem pertahanan dirinya dengan cara kamuflase dan menggunakan senyawa kimia sebagai racun yang didapat dari makanannya. Tujuan dari penelitian ini yaitu mendapatkan isolat bakteri yang bersimbiosis dengan P. nigra, mendapatkan ekstrak dari baktri simbion, dan menguji antibakteri dan anti-UV ekstrak etil aseta bakteri simbion dengan metode difusi agar terhadap bakteri Escherichia coli dan Bacillus megaterium. Hasil penelitian didapatkan kelima isolat yang diuji memiliki aktivitas antibakteri dengan rerata zona hambat tertinggi terhadap bakteri E. coli DSM 498 yaitu isolat 1 (14,67 mm), isolat 5 (14 mm), dan terhadap baktri B. megaterium DSM 32T yaitu isolat 3 (13,33 mm). Ketiga isolat yang memiliki zona hambat tertinggi dan ekstrak P. nigra diujikan anti-UV menggunakan alat UV-Vis Spektrofotometer. Hasil yang didapat isolat 3 memiliki serapan terhadap radiasi sinar UV-A dengan puncak tertinggi pada λ 340 nm dan ekstrak P. nigra memiliki serapan terhadap radiasi sinar UV-B dengan puncak tertinggi berada pada λ 290 nm. Kata kunci: Nudibranchia, Bacteria, Anti-bacteial, Anti-UV]]>
