AbstractAsperchalasine A (1), the first cytochalasan dimer featuring a unique decacyclic 5/6/11/5/5/6/5/11/6/5 ring system consisting of 20 chiral centers, was isolated from the culture broth of Aspergillus flavipes. Three biogenetically related intermediates, asperchalasines B–D (2–4), were also isolated. Their structures, including their absolute configurations, were elucidated using a combination of HRESIMS, NMR, ECD, molecular modeling, and single‐crystal X‐ray diffraction techniques. Compound 1, which possesses an unprecedented 13‐oxatetracyclo[7.2.1.12,5.01,6]tridec‐8,12‐dione core structure, is the first example of a dimeric cytochalasan alkaloid. The biogenetic pathways of 1–4 were described starting from the co‐isolated compounds 5 and 6. More importantly, 1 induced significant G1‐phase cell cycle arrest by selectively inhibiting cyclin A, CDK2 and CDK6 in cancerous, but not normal, cells, highlighting it as a potentially selective cell cycle regulator against cancer cells.