Abstract-In present work, hierarchical flower-like ZnO particles (FL-ZnO) were synthesized by organic-free hydrothermal route. The hexagonal structure and the formation of flower-like structure of FL-ZnO were observed by XRD and SEM analysis, respectively. The adsorption capability of FL-ZnO for the anionic (Sunset Yellow) and cationic (Malachite Green) dyes was investigated in a batch process. The effects of initial pH, initial dye concentration, temperature, and adsorbent concentration on the studied adsorption processes were also evaluated and the results showed that the studied adsorption systems were noticeably dependent of initial pH in the experimental range. The adsorption mechanism was described by the equilibrium, kinetic, and mass transfer modelling. The results showed that the experimental equilibrium data for both dyestuff were fitted well to Langmuir isotherm model, the studied adsorption kinetics were in the best agreement with the pseudo second order model, both intraparticle and film diffusion were effective on the studied adsorption systems as to Weber-Morris model. Besides, the antibacterial activities of FL-ZnO for the gram negative Escherichia-coli (O157: H7) and the gram positive Listeria monocytogenes were tested.Index Terms-Adsorption, adsorbent, antibacterial activity, hierarchical flower-like ZnO, metal oxide materials.