In this study, the impacts of doping concentration on the crystal structure, morphology, electrical, and optical properties of Ho3+-doped zinc oxide (ZnO) nanorod (NR) arrays were studied. Structural and morphological characterizations showed that the Ho3+-doped ZnO NRs were crystallized in the (002) direction, and that they had a homogeneous distribution on the substrate. The crystallite sizes of the samples were between 50 nm and 65 nm. SEM analysis showed that every sample was hexagonal in shape. For the 1 and 5 mol.% Ho3+-doped ZnO NRs, the values for electrical conductivity were found to be 1.41 x 10(-7) and 8.29 x 10(-6) (omega cm)(-1) at 25 degrees C and 1.70 x 10(-5) and 1.24 x 10(-3) (omega cm)(-1) at 300 degrees C, respectively. The optical transmittances were between 80 and 93% for all the samples in the region from 400 to 1000 nm. The optical band gap values were determined to be between 3.180 and 3.195 eV.