Perpendicularly arrayed and size-controlled nanocylinders have been prepared by simply blending an asymmetric polystyrene-block-polyisoprene-block-polystyrene triblock copolymer with polystyrene (the minority component) homopolymers of different molecular weights. The preference for perpendicular orientation or hexagonal ordering of the nanocylinders over a large area in the asymmetric block copolymer can be controlled by adjusting the molecular weight of the blended homopolymer, and the perfection of hexagonal ordering of the perpendicular cylinders can be tuned by using a substrate whose surface tension is much different from that of the majority component of the block copolymer. Such highly controlled nanostructured block-copolymer materials, which have been obtained by a simple method independent of film thickness and interfacial tension between the blocks and the substrates, have wide-ranging commercial potential, e.g., for use in membranes and nanotemplates with size-tunable pores, bandgap-controlled photonic crystals, and other nanotechnological fields demanding a specific nanosize and nanomorphology.