Zinc oxide, a well-known inorganic metal oxide, in nanoparticle form exhibits photo-catalysis, antimicrobial behavior and is also employed in energy cells as well as sensor devices. In the present study, zinc oxide nanoparticles (ZnO NPs) were synthesized using Adathoda beddomei (A. Beddomei) leaf extract as well as Plectranthus barbatus (P. Barbatus) leaf extract. X-ray diffraction studies confirmed the presence of hexagonal wurtzite structure of ZnO NPs having the least particle size ∼18–24 nm, with preferential growth along (101) plane. The UV–visible absorbance spectrum of ZnO NPs exhibited the absorbance band in the range 371– 375 nm. Photo luminescence spectra dominated by a strong luminescence peak at ∼384–394 nm followed by low intensity peaks at ∼444–487 nm. Fourier transform infrared spectra confirmed the presence of ZnO NPs as well as the functional groups of plant extracts. Antibacterial properties of synthesized ZnO NPs were evaluated against Gram-negative bacteria–Escherchia coli (E. coli) and Gram-positive bacteria–Listeria monocytogenes. Both bio-synthesized ZnO NPs exhibit significant antibacterial activity only against E. coli. The zones of inhibition were found to be 7 mm and 9 mm for A. Beddomei and P. Barbatus respectively. This study demonstrates utilization of A. Beddomei and P. Barbatus leaf extract for the efficient synthesis of ZnO NPs using a biosynthesis method to obtain significant antibacterial activity.