Emethacins A (1) and B (2), sulfur-containing dioxopiperazines, were isolated from Emericella heterothallica ATCC 16824, along with three dioxopiperazine derivatives (3-5). Emethacin B was identical with (3S,6R)-3,6-dibenzyl-3,6-bis(methylthio)-2,5-dioxopiperazine (2) which had been already isolated from Aspergillus s. The structure of the new compound, emethacin A (1), was confirmed by spectroscopic and chemical correlation as (3R,6Z)-3-benzyl-6-benzylidene-3-methylthio-2,5-dioxopiperazine. Compound 3 was (3S,6Z)-3-benzyl-6-benzylidene-2,5-dioxopiperazine, which was the enantiomer of the compound 7 isolated from Streptomyces noursei.