Green synthetic methods of nanoparticles are simple, non-Toxic and environmentally benign process which decline the demerits of conventional physical and chemical methods. The current study focusses on the synthesis of zinc oxide nanoparticles using fresh Brassica oleracea extract. Zinc oxide nanoparticles were characterized using UV-vis spectrophotometry, which showed exciton absorption peak at 380 nm. X-ray diffraction analysis, scanning electron microscopy, atomic force microscopy, energy dispersive X-ray analysis and thermogravimetric analysis were used to determine the shape, size, crystallinity and purity of nanoparticles. The antibacterial activity of zinc oxide nanoparticles was determined by agar well diffusion method against Gram-positive and Gram-negative bacteria. © 2018 Chemical Publishing Co. All rights reserved.