The fabrication and catalytic application of a size-tunable monodisperse nanoparticle array enabled by block copolymer lithography is demonstrated. Highly uniform vertical cylinder nanodomains are achieved in poly(styrene-block-4-vinylpyridine) (PS-b-P4VP) diblock copolymer thin-films by solvent annealing. The prominent diffusion of the anionic metal complexes into the protonated P4VP cylinder nanodomains occurs through specific electrostatic interactions in a weakly acidic aqueous solution. This well-defined diffusion with nanoscale confinement enables preparation of the laterally ordered monodisperse nanoparticle array with sub-nanometer level precise size tuning. The controlled growth of monodisperse nanoparticle arrays is proven by their catalytic use for vertical carbon nanotube (CNT) growth via plasma enhanced chemical vapor deposition (PECVD). Since the size of the catalyst particles is the decisive parameter for the diameters and wall-numbers of CNTs, the highly selective growth of double-walled or triple-walled CNTs could be accomplished using monodisperse nanoparticle arrays.