Zinc oxide (ZnO) nanoparticles attract researchers' attention because of their non-toxicity and multi-potential applications. To synthesize ZnO nanoparticles, various physical, chemical and green methods have been used. In this study, Zinc Oxide nanoparticles were prepared via three different techniques using the zinc nitrate solution as a precursor in a comparative study. The three methods classified Sol-gel and precipitation as chemical methods and environmentally friendly Leidenfrost green synthesis techniques. The resulting samples are characterized by X-ray diffraction analysis (XRD), Fourier Transform Infrared (FTIR) spectroscopy and UV-Visible (UV–Vis) optical absorption. The XRD analysis approves the formation of ZnO nanoparticles for the three methods with the same peaks' orientation (100), (002), (101), (102), (110), (103) and (112) planes. The crystallite size was determined instrumentally to be 17.2, 27 and 65 nm for Sol-gel, Precipitation and Leidenfrost methods, respectively. The results of XRD analysis approve that the chemical methods give the smallest crystallite size whereas the green one shows the highest crystallinity compared with chemical methods. FTIR spectra peaks showed the characteristic transmittance band of the ZnO nanoparticles. The UV-Visible spectrum showed the band gaps of synthesized samples 3.3, 2.03 and 3.2 eV for Sol-gel, Precipitation, and Leidenfrost methods, respectively.