We demonstrate an efficient possibility to synthesize vertically aligned pure zinc oxide (ZnO) and Co-doped ZnO nanorods (NRs) using the low-temperature aqueous chemical synthesis (90 C). Two different mixing methods of the synthesis solutions were investigated for the Co-doped samples. The synthesized samples were compared to pure ZnO NRs regarding the Co incorporation and crystal quality. Electron paramagnetic resonance (EPR) measurements confirmed the substitution of Co 2þ inside the ZnO NRs, giving a highly anisotropic magnetic Co 2þ signal. The substitution of Zn2þ by Co 2þ was observed to be combined with a drastic reduction in the core-defect (CD) signal (g 1.956) which is seen in pure ZnO NRs. As revealed by the cathodoluminescence (CL), the incorporation of Co causes a slight red-shift of the UV peak position combined with an enhancement in the intensity of the defect-related yellow-orange emission compared to pure ZnO NRs. Furthermore, the EPR and the CL measurements allow a possible model of the defect configuration in the samples. It is proposed that the assynthesized pure ZnO NRs likely contain Zn interstitial (Zn iþ) as CDs and oxygen vacancy (V O ) or oxygen interstitial (O i) as surface defects. As a result, Co was found to likely occupy the Zn iþ, leading to the observed CDs reduction and hence enhancing the crystal quality. These results open the possibility of synthesis of highly crystalline quality ZnO NRs-based diluted magnetic semiconductors using the low-temperature aqueous chemical method