The effect of nanostructured ZnO thin films on one Gram positive and one Gram-negative bacterium is studied. The films are prepared by different methods: (i) RF magnetron sputtering of ZnO target in atmosphere of Ar (0.5 Pa ) or Ar (0.5 Pa )+H2 (0.1Pa ), (ii) Sol-gel – glass substrate is dip coated in a colloidal sol prepared from zinc acetate, dried and then fired at high temperature in order to get thin ZnO films; (iii) Chemical deposition – seeds of ZnO are first casted on a glass substrate and then ZnO nanorods are repeatedly grown on them via deposition from a chemical bath. The ZnO films structures are studied by XRD, SEM and AFM. All patterns have a polycrystalline structure with preferential (002) crystallographic orientation and c-axis perpendicular to the substrate surface. The influence of the as-prepared films on Bacillus cereus and Pseudomonas putida is studied by two different methods - optical density measurement and classic cultivation (rich and poor medium). Periodic cultures of bacteria are investigated in a 24-hours experiment for sensitivity to the ZnO thin films immersed in the bacterial suspension. Our experiments prove that ZnO films made by wet colloidal methods (sol-gel or chemical bath) are toxic to the studied bacteria. The ZnO thin films obtained by r.f. magnetron sputtering activate the rate of cell division and increase the percentage of live cells in comparison with the control experiment (without ZnO film). The observed difference can be due to the release of zinc species from the colloid-made films.