To investigate cytotoxic secondary metabolites of Micrococcus sp. R21, an actinomycete isolated from a deep-sea sediment (-6 310 m; 142 degrees 19. 9' E, 10 degrees 54. 6' N) of the Western Pacific Ocean, column chromatography was introduced over silica gel, ODS, and Sephadex LH-20. As a result, eight compounds were obtained. By mainly detailed analysis of the NMR data, their structures were elucidated as cyclo(4-hydroxy-L-Pro-L-leu) (1), cyclo(L-Pro-L-Gly) (2), cyclo( L-Pro-L-Ala) (3), cyclo( D-Pro-L-Leu) (4), N-β-acetyltryptamine (5), 2-hydroxybenzoic acid (6), and phenylacetic acid (7). Compound 1 exhibited weak cytotoxic activity against RAW264. 7 cells with IC50 value of 9.1 μmol x L(-1).