The aim of this research was to prepare a different particle sizes of zinc oxide nanostructures by two different methods. The zinc oxide nanoparticle (ZnO NPs) was successfully prepared by a green synthesis technique but the zinc oxide quantum dot (ZnO QDs) was successfully prepared by a chemical method. The structure, composition and morphology of the prepared different shapes of ZnO nanostructures have been characterized by the means of X-ray diffractograms (XRD), high resolution transmission electron microscope (HRTEM), Energy Dispersive x-ray (EDX), UV-Vis spectroscopy and Fourier transform infrared spectroscopy (FTIR). From UV-Vis spectroscopy studies we noticed that the optical band gap energy of ZnO nanostructures was decreased by increasing an irradiation time. The removal of complex organic contaminants and pollutants from water, the heterogeneous photocatalytic degradation of methylene blue (MB), Fluorescein and Rhodamine 6G (Rh 6G) dyes were studied using ZnO NPs and ZnO QDs as a derived catalyst. We had studied the impact of ZnO NPs and ZnO QDs as a catalyst to enhance the photocatalytic activity of different organic dyes under UV-Vis irradiation and we observed that the photodegradation percentage of organic dyes was rapidly increased by increasing UV irradiation time in both two shapes of ZnO nanostructures. ZnO QDs behave as the best photocatalyst for successfully photodegraded due to the smallest size of ZnO QDs has a higher photocatalytic activity than the large particle size of ZnO NPs. So, it is better to use the ZnO QDs as a removal dyes and pollutants in the wastewater application. Also, we have assessed the cytotoxicity of ZnO NPs and ZnO QDs against two cell lines, (T-47) breast cancer carcinoma, and (DU-145) prostate cancer cell compared to Human skin fibroblast (HSF). The proliferation of cancer cells using MTT assay clarified that both cancer cells (T-47), (DU-145) as well as (HSF) normal cell line are regularly inhibited as they grow on different concentrations of ZnQ QDs and ZnQ NPs. The maximum inhibitory effect of both were recorded at concentration of 100 µg/ml (62.63, 79.72 and 42.59% and 72.68, 83.28, 18.12 µg/ml) in case of ZnQ QDs and ZnQ NPs respectively. It was cleared that ZnQ NPs was more potent for test cancer cell lines, this was confirmed by IC50, since it was (18.12,13.3,74.86) in ZnO NPs compared with (42.59,17.05 and 76.4) in ZnQ QDs respectively. Finally, it was proved that the ZnO NPs behave as a good anticancer nanomaterial than ZnO QDs. This means ZnO NPs are superior for anticancer applications if compared with ZnO QDs.