Four new diketopiperazine alkaloids, rel-(8R)-9-hydroxy-8-methoxy-18-epi-fumitremorgin C (1), rel-(8S)-19,20-dihydro-9,20-dihydroxy-8-methoxy-9,18-di-epi-fumitremorgin C (2), rel-(8S,19S)-19,20-dihydro-9,19,20-trihydroxy-8-methoxy-9-epi-fumitremorgin C (3), and (3S,8S,9S,18S)-8,9-dihydroxyspirotryprostatin A (4), together with the eight known compounds 512, were isolated from the endophytic fungus Aspergillus fumigatus. The structures of the new compounds were determined by extensive spectroscopic methods including HR-ESI-MS, NMR, and CD experiments. Compound 12 showed weak inhibitory activity in vitro against the release of beta-glucuronidase in rat polymorphonuclear leukocytes induced by the platelet-activating factor. None of the twelve compounds exhibited detectable cytotoxic activities toward five human tumor cell lines (HCT-8, Bel-7402, BGC-823, A549, and A2780) in the MTT assay.