Uniform, vertically aligned ZnO nanorods have been grown mainly on Au-coated and ZnO-coated sapphire substrates, ZnO-and GaN-coated substrates, or self-catalyzing substrates. Conventionally, Ni-coated substrates have resulted in thick rods with diameter more than 250 nm, rods with nonuniform distribution in diameter, or rods with an alignment problem. In the best result in this paper, slender, uniform, vertically aligned, solely UV-emitting ZnO nanorods with diameter of 110 ± 25 nm and length of 30 ± 10 lm have been successfully grown at 700°C for 2 h on sapphire substrates covered with Nibased buffer layers by using metallic zinc and oxygen as reactants. Scanning electron microscopy and room-temperature photoluminescence have been used to investigate the effects of process conditions on the slenderness and vertical alignment of the ZnO rods. To develop the desired ZnO nanorods, etched sapphire substrates, a second metallic Sn buffer layer on top of a spin-coated nickel oxide layer, polyvinyl alcohol binder at 10% concentration in solution of iron nitrate, and pyrolysis and reduction reactions were involved. Defect photoemission for thick ZnO rods is attributed to insufficient oxygen supply during the growth process with fixed oxygen flow rate.