New diketopiperazines, epicoccins E-H (1-4) and diphenylalazines A (5) and B (6), have been isolated from the solid-substrate fermentation culture of the Cordyceps-colonizing fungus Epicoccum nigrum. The structures of 1-6 were determined primarily by NMR experiments, and the structure of 1 was confirmed by X-ray crystallography. The absolute configurations of 3 and 5 were assigned using the modified Mosher (3) and Marfey's (5) methods, respectively. Compounds 3-5 showed inhibitory effects on HIV-1 replication in C8166 cells.