Polyoxometalates are nanosized metal-oxygen macroanions and suitable building blocks of ionic crystals with nanostructures in combination with appropriate macrocations. In this review, (1) formation of ionic crystals by the complexation of the polyoxo-metalates with a macrocation and the hydrophilic guest sorption properties, (2) effects of charges of polyoxometalates on the structures and sorption properties of ionic crystals, and (3) construction of both hydrophilic and hydrophobic channels in the crystal lattice of the polyoxometalate based ionic crystals are highlighted.