The self-assembly and the formation of "Blackberry" type supramolecular structures for a type of Yttrium-containing polyoxometalate(K15Na6(H3O)(9)[(PY2W10O38)(4)(W3O14)center dot 9H(2)0, or {P4Y8W43}) macroanions is characterized by using static and dynamic light scattering techniques. {P4Y8W43} macroions are found to form hollow, spherical, single-layer "blackberry" structures in water and water-acetone mixed solvents. Very interestingly, the blackberry size can be accurately controlled by either changing acetone content in water-acetone mixed solvents, or by changing solution pH in aqueous solution. The blackberry size increases with decreasing pH (lower charge density) or higher acetone content in the mixed solvent (lower dielectric constant) and the blackberry size can change in responding to the change of external conditions. This indicates that the {P4Y8W43} macroanions possess the properties of both "strong electrolyte type" and "weak electrolyte type" macroions, as we outlined previously. This is due to the special chemical feature of such clusters, which can be treated as Na2HPO4-type electrolytes in solution. The kinetics of the blackberry formation can be controlled by temperature.