Zinc oxide nanoparticles (ZnO NPs) were green synthesized using Pelargonum zonale leaf extract under three different heating methods, and their characteristics were evaluated using X-ray diffractometry (XRD), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), 2,2-diphenyl-2-picrylhydrazyl (DPPH) assay and antibacterial well diffusion method. The FT-IR analysis indicated that the Pelargonium leaf extract contained hydroxyl and amide I groups which were related to the proteins, carbohydrate, tannins and phenolic compounds of the extract and had an essential role in the reduction of the zinc ions and synthesis of the ZnO NPs. The obtained results revealed that the synthesized spherical individual ZnO NPs as well as the number of aggregates using microwave irradiation, autoclave and conventional heating (heater-stirrer) methods had average crystalline size of 51, 60 and 61 nm. Furthermore, antioxidant activities of the fabricated ZnO NPs were 7.8, 4.1 and 5.5% by using conventional heating, autoclave and microwave irradiation, respectively. The obtained results indicated that all the formed ZnO NPs had bactericidal effects against to the both Gram negative and Gram positive bacteria strains. However, the synthesized ZnO NPs using conventional heating method had the highest antibacterial activities toward both studied bacteria strains.