The effect of thiourea on the electrochemical deposition of zinc oxide is investigated using zinc nitrate aqueous solutions. The effect of thiourea concentration between 0 and 1.0 M is first evaluated from a theoretical solution chemistry analysis, showing that zinc ions are consistently complexed by the thiourea for pH < 6. Cyclic voltammetry studies using SnO2:F and ZnO:Al coated glass conducting substrates are carried out in order to define the deposition potential domain. Compositional and structural analyses show that the deposited films are constituted of crystalline ZnO layer and very low incorporation of sulfur is observed. Moreover, as soon as 0.05 M of thiourea is added, films seem to be much thicker than expected from the apparent Faradaic efficiency calculations. Based on these results it seems that thiourea could be a suitable additive for the formation of nanoporous films. The role of thiourea in zinc nitrate aqueous solutions is discussed in relation to solution chemistry analysis. (C) 2015 Elsevier Ltd. All rights reserved.