Blanket-like assembled ZnO nanowhiskers were fabricated using a freestanding ZnO nanoparticle layer by an aqueous solution deposition. X-ray diffraction and field emission scanning electron microscopy clarified the crystalline phase, orientation, morphology, and microstructure. Thermal treatment of the zinc acetate dihydrate layer resulted in the formation and delamination of the ZnO nanoparticle layer on the glass substrate. The growth habits of ZnO crystals resulted in the growth of ZnO nanowhiskers preferentially orientated along the direction of the c-axis on the whole surface of the freestanding ZnO nanoparticle layer by heterogeneorous nucleation and growth. The hierarchical-structured blanket-like ZnO nanowhisker assemblies can be utilized for dye-sensitive solar cells and gas sensors because of their high surface-to-volume ratio.