The objective of this study is to synthesize ZnO nanoparticles (ZnO NPs) using Ipomoea carnea flower extract for the first time and investigate its antibacterial activity. The study on the antibacterial activity of ZnO NPs against gram positive bacteria (Staphylococcus aureus, Bacillus subtilis), and gram negative bacteria (Klebsiella pneumoniae, Escherichia coli) reveals that the material prepared has good antibacterial efficacy. The mechanism behind the antibacterial efficiencies have been discussed in detail. The results obtained through UV-Visible spectroscopy, SEM, TEM, FT-IR spectroscopy support well the mechanism proposed.