Three new dioxopiperazine metabolites (1-3), together with two known compounds, N-acetyltyramine (4) and cyclo-(Ala-Val) (5), were isolated from a marine-derived fungus Aspergillus fumigatus Fres. Their structures were established by spectroscopic methods. Their cytotoxic activities against the K562 cell line were preliminarily evaluated by the sulphorhodamine B (SRB) method.