An epitetrathiodioxopiperazine, secoemestrin C, related to the macrocyclic antifungal epidithiodioxopiperazine, emestrin, originally isolated from Emericella striata and E. quadrilineata, was isolated along with the epitrithiodioxopiperazine, emestrin B, from the culture medium of the early state of E. foveolata. This fungus also produced emestrin in the mycelium and dethiosecoemestrin and violaceic acid in the culture broth after two weeks cultivation. The structure of secoemestrin C was established by spectroscopic and chemical investigation. Secoemestrin C may be the key intermediate from emestrin and/or emestrin B to dethiosecoemestrin.