Zinc oxide (ZnO) nanoparticles were synthesized by using wet chemical method. The synthesized sample was characterized by X-ray diffraction technique (XRD). The average crystallite size of the sample was calculated from the full width at half maximum of XRD peaks by using Debye-Scherrer’s formula and was found to be 27 nm. E.coli was used as test microorganism. Disk diffusion method was used to determine the antibacterial activity of various classes of antibiotics in the absence and presence of zinc oxide nanoparticles. We also compared antibacterial activity of ZnO nanparticles and bulk ZnO. These results indicated that the ZnO nano particles potentiate bactericidal efficacy of fluoroquinolone, cephalosporin, carbapenum, polymixine and amino glycoside antibiotics.