Nanoscaled polyoxometalate (POM) clusters represent the largest inorganic molecules known so far. It is our common sense that soluble inorganic ions distribute homogeneously in dilute solutions, and anions attract cations and repel other anions. But these obvious facts become questionable when the ions are large (macroions). Many type of giant hydrophilic POM anions are highly soluble, but strongly attract with each other and form uniform, single-layer vesicle-like “blackberry” structures containing >1000 individual POM anions in dilute solutions. The blackberry structure represents a new but universal type of self-assembly, favored by macroions. Its driving force is totally different from other types of self-assembly. Many exciting new phenomena, such as the soft, biomembrane nature of the blackberry shells, have been observed. The hydrophilic maroionic solutions offer a direct connection between traditional fields such as simple inorganic ions, colloids and biomacromolecules. Particularly, the blackberry structure might mimic the virus shells formed by capsid proteins. Now the fundamental questions on “what happens when soluble inorganic ions reach the size of nanometer scale?” and “What is the transitional stage between simple ions and colloid suspensions” can be addressed. Furthermore, the blackberry structures might find broad applications as nanocontainers and nanoreactors with tunable size and unique permeability and mechanical strength.