Marine organisms, especially marine microorganisms, have been proven to be a rich source of diverse arrays of bioactive metabolites with great potential for pharmaceutical and medical applications. Marine Bacillus subtilis is a common strain species, which usually produces cyclopeptide, macrolide, indole derivatives, etc. In the course of further studies, 10 diketopiperazines: cyclo(Leu-Ile) (1) [1], cyclo(Leu-Leu) (2) [2], cyclo(Trp-Pro) (3) [3], cyclo(Leu-Pro) (4) [4, 5], cyclo(Phe-Ala) (5) [6], cyclo(PheTyr) (6) [2], cyclo(benzyl-Gly) (7) [7], cyclo(Val-Val) (8) [8], cyclo(Gla-Tyr) (9) [9], cyclo(Ala-Tyr) (10) [10], 1-(4-hydroxyphenyl)ethanone (11) [11], and macrolactin B (12) [12] have been isolated from the marine Bacillus subtilis. Among them, compound 7 is a new natural product. All the compounds have not been reported before from this species. The strain 201721 has been derived from sea sediment of East Sea of China. It was isolated on F1 medium [Glucose (6 g), peptone (5 g), and yeast extract (1 g) were dissolved in artifical seawater (1L)] with incubation for 4 days at 28°C. Due to its chemical and morphological features as well as the 16S rDNA (GenBank accession number EF417872), the strain can be identified as the genus Bacillus sp. Chemistry of Natural Compounds, Vol. 45, No. 2, 2009