In present work the antibacterial activity of chemically synthesized Zinc oxide nanoparticles and their synergistic effect with antibiotics on six pathogenic bacteria was analyzed. The nanoparticles were characterized by high resolution SEM (Scanning Electron Microscopy), FTIR (Fourier Transform Infra-Red spectroscopy) and UV-VIS analytical techniques to probe their structure, surface morphology and physical characteristics. When ZnO NPs were applied alone at various concentrations in Pseudomonas aeruginosa, Bacillus subtilis, Salmonella typhimurium, Streptococcus spp., Klebsiella spp. and E. coli cultures, it was observed that minimum zone of inhibition in E.coli i.e. 0.4 cm and maximum growth inhibition in Klebsiella spp. i.e. 3.4 cm. Thereafter, antibiotic effect was monitored with three antibiotics, namely, gentamicin, ciprofloxacin and ampicillin. Among all the six bacteria, Klebsiella spp. was highly sensitive to all the three antibiotics and Streptococcus spp was most sensitive to ampicillin. When the synergistic effect of ZnO NPs in combination with three antibiotics was observed it revealed the maximum growth inhibition in Pseudomonas aeruginosa with combination of ZnO NPs and chlorofloxacin, followed by combination of ZnO NPs and gentamicin in E.coli, combination of ZnO NPs and ampicillin in E.coli. All the bacterial species exhibited more than 300 per cent augmentation in growth inhibition.