Seven new fumiquinazolines (FQs) A-G have been isolated from a strain of Aspergillus fumigatus originally separated from the marine fish Pseudolabrus japonicus, and their stereostructures and conformations have been established on the basis of spectral and X-ray analyses and some chemical transformations. All the compounds exhibited moderate cytotoxicity against cultured P388 cells. Based on the fact that some of the bioactive materials isolated from marine animals have been produced by bacteria, we have focused our attention on new antitumour materials from microorganisms inhabiting the marine environment. As part of this program, we previously reported that antitumour and cytotoxic compounds were produced by microorganisms originally isolated from the marine fish Halichoeres bleeki and the marine algae Enteromorpha intestinalis and Sargassum tortile and that their structures had been established. In our continuing search for cytotoxic compounds from marine microorganisms, we have isolated seven metabolites designated fumiquinazolines (FQs) A-G 1-3 and 7-10 from a strain of Aspergillus fumigatus separated from the gastrointestinal tract of the marine fish Pseudolabrus japonicus. We report herein the isolation and structure determination of compounds 3,7,8 and 10 and the details of the structure elucidation of compounds 1,2 and 9, already briefly reported in a preliminary form.