In the course of a search for metabolites related to emestrin (2) from Emericells striata, a new compound designated emestrin B (1) was isolated, together with shamixanthone, from the mycelial acetone extract. Shamixanthone is a compound related to emericellin, which had previously been isolated from the mycelium of the above fungus. The structure of emestrin B (1), including its absolute configuration, was established on the basis of the spectroscopic investigations. Emestrin B (1) is an epitrithio derivative corresponding to the antifungal macrocyclic epidithiodioxopiperazine, emestrin (2).