The study of Aspergillus micronesiensis led to the isolation of three unprecedented cytochalasans (1-3). Dimericchalasine A (1) is the first cytochalasan homodimer fused by a C-20/C-20' single bond. Amichalasines D (2) and E (3) represent a new type of cytochalasan heterotrimer with a decacyclic 5/6/11/5/5/6/5/12/6/5 ring system. Their structures were determined by extensive spectroscopic data and single-crystal X-ray diffraction. The plausible biosynthetic pathways of 1-3 were proposed.