The first mixed-valence silver(I,III) cryptate, [AgAgO(C42H54N8)](ClO4)2 (C42H54N8 denotes the crypt and ligand), was prepared by (2 + 3) condensation of tris(3-aminopropyl)amine and terephthalaldehyde in the presence of silver(I) ion. The crystal structure reveals the formation of a Ag(III)=O bond with distance 1.586(4) angstrom, being consistent with the reported M=O bond length of transistion metals. This shows that the silver atom activated and cleaved an oxygen molecule in this macrobicyclic compound. Hitherto the only mixed-valence silver(I,III) compound has been silver(I,III) oxide.