Large-area vertically orientated and high-density ZnO nanorod arrays (NRAs) have been electrochemically grown directly onto IZO:Ga thin film transparent conductive oxide (TCO) substrates. For the sake of comparison, ZnO NRAs have also been electrodeposited onto conventional TCO/glass substrates (F-doped SnO2(FTO) and Sn-doped In2O3(ITO). The morphological and structural properties of the resulting ZnO NRAs have been studied. The nucleation and growth mechanism (NGM) that governs the electrochemical growth of these ZnO nanostructures onto these TCO substrates were investigated, demonstrating that the IZO:Ga thin film triggers the orientated and structured growth of ZnO nanorods. ZnO nanorods of ca. 225 nm, 256 nm and 259 nm in diameter and ZnO NRAs densities values of 2.05 x 10(8)cm(-2), 2.27 x 10(8)cm(-2)and 7.83 x 10(8)cm(-2)have been obtained when deposited onto these FTO, ITO and IZO:Ga thin film substrates, respectively. NGM study results indicate that onto FTO and ITO after an initial current decay (following a Cottrell law), a 3D instantaneous nuclei formation limited by lattice incorporation takes place. Whereas onto the IZO:Ga substrate, at the early stages a new contribution 3D instantaneous nucleation under diffusion control, appeared, revealing that these densely packed IZO:Ga nanocrystals may act as homo-epitaxial nucleation sites.