An adamantane-based cage with a three-dimensional (3D) framework was synthesized by the copper-mediated acetylene coupling reaction, in which two 1,3,5-triethynyladamantane units were linked by phenyldiacetylenic bridges possessing ester groups. X-ray crystallography revealed that the cage has an internal space and accommodates a solvent molecule, which afforded molecular networks through CH/O interactions between cage molecules. Furthermore, the cage containing six ester groups spontaneously self-assembled into hollow spherical aggregates with an average diameter of 230 nm in a mixed solvent.