Eight new thiodiketopiperazines, designated as graphiumins A to H (1-8), were isolated along with bisdethiobis(methylthio)-deacetylaranotin (9) and bisdethiobis(methylthio)-deacetylapoaranotin (10) from the culture broth of the marine-derived fungus Graphium sp. OPMF00224. The structures of the graphiumins were elucidated based on spectroscopic analyses (1D and 2D NMR data, ROESY correlations and CD data) and chemical methods. The absolute configuration of the common (3S)-3-hydroxy-octanoyl acid residue in 1, 3 and 4 was determined by hydrolysis, benzoyl derivatization and HPLC analysis using a chiral column. Five graphiumins moderately inhibited yellow pigment production by methicillin-resistant Staphylococcus aureus.