Two new diketopiperazine derivatives, staphyloamides A (1), and B (2), have been isolated from the culture broth of Staphylococcus sp. (No. P-100826-4-6) derived from Corallina officinalis Lineaus, along with the known cyclo (L-pro-D-phe) (3), cyclo (D-6-Hypro-L-phe) (4), cyclo (L-pro-L-val) (5), cyclo (L-pro-L-phe) (6), cyclo (L-pro-L-tyr) (7), cyclo (L-pro-L-leu) (8), cyclo (L-pro-L-ala) (9), and bacillusamide B (10). These structures were elucidated by extensive spectroscopic methods. Antimicrobial activities of compounds 3–10 were done.