The present report an environmental benign route for the fabrication of Zinc Oxide nanoparticles (ZnO-NPs) using sunflower leaf aqueous extract at room temperature. This was an green method is a rapid biogenic and offers few advantages over the chemical and physical procedures, as it is an easy and fast, eco-friendly and does not involve any costly chemicals as well as hazardous chemicals, harmful solvent. The synthesized ZnO-NPs were characterized using different technique such as UV-Visible spectroscopy. The formation of ZnO-NPs was confirmed by Surface Plasmon Resonance (SRP) at 344 nm using UV-Vis spectroscopy. The leaf extract act as a source of phyto-chemicals and are the primarily responsible for the reduction and then formation of stable Zinc Oxide nanoparticles by the characteristic functional groups of extract and synthesized ZnO-NPs were identified by FTIR spectroscopy. Crystalline nature of ZnO-NPs was confirmed by powder –XRD. Size and morphology were measured by HR-TEM analysis. Stability of the nanoparticles is represented by DLS and TGA analysis. The synthesized ZnO-NPs has been found good and efficient catalyst for the synthesis of novel 1,2-dihydroquinazoline derivatives under green method via one pot reaction of 2-amino benzophenone, 1,3-diphenyl-1 H -pyrazole carbaldehydes and ammonium acetate. The synthesized compounds (4a-o) were characterized by 1 HNMR, 13 CNMR and HRMS spectra and further screened for radical scavenging activity. Among all the compounds showed good percentage of inhibition against standard ascorbic acid. The synthesized ZnO nanoparticles showed good antioxidant activity and also act as a good promising material for catalytic agent.