Abstract: In this study, a sustainable method using the aqueous extract of Crataegus spp. was developed for producing zinc oxide (ZnO) nanostructures. The leaves and fruits of the plant were used to prepare the aqueous extracts through ultrasonic-assisted extraction, which were then utilized for the eco-friendly synthesis of ZnO. Analysis of the resulting nanostructures using X-ray diffraction and scanning electron microscopy confirmed the hexagonal structure of ZnO, with a size range of 40-70 nm. The absorption results show a clear and broad absorption band in the range of 275-400 nm for nanostructures synthesized from leaf and fruit extracts. The antibacterial properties of the synthesized ZnO nanostructures were investigated using the well diffusion method, revealing higher antibacterial activity compared to the plant's leaf and fruit extracts. Furthermore, the total phenol, flavonoid content, and antioxidant activity of the ZnO nanostructures and the extracts were studied and compared. The results indicated that the plant extracts exhibited greater antioxidant properties than the ZnO nanostructures. Additionally, toxicity tests were conducted on allium cepa samples to assess the toxicity of the samples. The ZnO nanostructures were then employed as effective nanocatalysts in Hantzsch reactions involving various aldehydes, such as ethyl acetate, ammonium acetate, and dimedone. The results demonstrated the synthesis of high-efficiency products (95%) within 2 hours using 0.02 g of nanocatalyst.