Reactions between two novel hexatopic carboxylate ligands and copper salts give rise to two isostructural metal-organic frameworks (MOFs) with a (3,24)-connected network topology containing both micro- and mesocavities with sizes of up to 3 nm. Both frameworks retain their porosity after guest-molecule removal, leading to high surface areas. Constructing MOFs containing mesocavities with microwindows may serve as a general approach toward stable MOFs with high surface areas.