Aim: In this study, the antibacterial activity of zinc oxide (ZnO) nanostructures of different shapes, including nanoparticles, nanoflowers and nanoflakes, was evaluated. Methods: The optical and morphological properties of the synthesized nanostructures were characterized by double-beam ultraviolet-visible (UV-Vis) analysis, X-ray diffraction (XRD) analysis, Energy Dispersive X-ray Analysis (EDX) and Scanning Electron Microscopy (SEM). Microdilution method was conducted, and minimum inhibitory concentration (MIC) was calculated to compare the antibacterial activity of the morphologically different nanostructures. Results: The SEM showed that ZnO-NPs were spherical in shape with a size of 100 nm. The EDX spectrum also showed that the synthesized ZnO-NPs were mainly composed of zinc, with the minimum contaminants being carbon and oxygen. The XRD analysis confirmed that the nature of the synthesized materials was ZnO with an average grain size of 3 nm to 21 nm. The greatest antibacterial activity of ZnO nanoparticles was against Pseudomonas aeruginosa, and for ZnO nanoflakes, against Escherichia coli. Conclusion: The study demonstrated that the antibacterial activity of nano-ZnO is shape-dependent.