Dithiosilvatin (1), an epidithiodioxopiperazine, and silvathione (2), a dioxopiperazinethione, were isolated from Aspergillus silvaticus, from the mycelial chloroform extract and the methylene dichloride extract of the culture filtrate respectively. Their structures were established on the basis of chemical reactions and spectroscopic evidence. Dithiosilvatin (1) is a very rare example of naturally occurring epidithiodioxopiperazines, a class of compounds which appear to be biosynthesized originally from glycine, and phenylalanine or tyrosine. Silvathione (2) is the second example of a natural dioxopiperazinethione and is biogenetically a possible key intermediate in the formation of trioxopiperazine from epidithiodioxopiperazine. The structure elucidation and the biogenetical importance of these compounds (1) and (2) are reported in this paper.