The predesigned metal-organic macrocycle Zn(3)QDB(3)(NO3)(4) (Zn-QDB) was observed to self-assemble into a hollow, spherical, single-layered "blackberry"-type structure. The self-assembly behaviors of the Zn-QDB are significantly influenced by additional small ions. Specifically, the cations exhibit strong co-ion effects on the interaction between cationic macrocycles which are different from the previously reported co-ion effects of simple anions on anionic polyoxometalates. This unusual phenomenon is due to the unique cation-pi interaction between small cations and electron-rich cavity of Zn-QPB, as confirmed by UV-vis, H-1 NMR, and fluorescence spectra. The variation of hydrodynamic radius (R-h) of assemblies with the changes of solution ionic strength and the, type of cations reveals the competition between counterion-mediated attraction and cation-pi interaction during the self assembly process. Furthermore, the cooperativity of cation-pi interaction and pi-pi stacking play a vital role in enhancing the stability of the supramolecular structure.