ObjectiveTo investigate the secondary metabolites of actinomycete Brevibacterium sp. associated with the sea cucumber Apostichopus japonicus Selenka. MethodsThe ethyl acetate extract of the actinomycete was purified by repeated column chromatography on silica gel, Sephadex LH-20, and high-performance liquid chromatography (HPLC) to obtain pure compounds; and the compound structures were elucidated by spectroscopic analysis (nuclear magnetic resonance, NMR; mass spectrometry, MS) and the results were compared with the previously reported data. ResultsSeven compounds were isolated: cyclo-(L-Pro-L-Phe) (1), cyclo-(L-Pro-L-Met) (2), cyclo-(L-Pro-L-Tyr) (3), cyclo-(L-Pro-L-Val) (4), cyclo-(L-Pro-L-Pro) (5), cyclo-(L-Val-Gly) (6), and cyclo-(L-Pro-L-Leu) (7). ConclusionThis is the first report on the secondary metabolites of microorganisms associated with the sea cucumber Apostichopus japonicus Selenka, and all the seven compounds have been reported from the actinomycete Brevibacterium sp. for the first time.