AbstractGuest‐induced M18L6–M24L8 capsule–capsule conversion is reported. Both capsules are composed of PdII ethylenediamine units (M) and 1,3,5‐tris(3,5‐pyrimidyl)pyrimidine (L), and form trigonal bipyramidal (M18L6) and octahedral (M24L8) closed‐shell structures with huge hydrophobic inner spaces. The M18L6 trigonal bipyramid is converted to the M24L8 octahedron through encapsulation of large aromatic guests, with the latter capsule possessing a cavity volume three times larger than the former. Despite the dynamic properties of the capsule host, the encapsulated guests are difficult to extract and are thus isolated from the external environment.