Nanotechnology is one of the most active research areas in modern material science. Nanotechnology can be termed as the synthesis, characterization, exploration and application of nanosized (1–100nm) particles for the development of science.Green synthesis of nanoparticles is an eco–friendly approach which might pave the way for researchers across the globe to explore the potential of different herbs in order to synthesize nanoparticles.Present investigation conducts a study on the synthesis and characterization of gold nanoparticles using Justiciaadhatoda.Antibacterial efficacy of the gold nanoparticles against 4 different bacteria, E.coli, Stapylococcus sp., Klebsiella sp., Pseudomonas sp.has been performed.The UV visible spectroscopy of the synthesized nano particles were in the range of 400–800 nm. The plant extract showed to synthesize the gold nanoparticles by the indication of suitable surface Plasmon resonance (SPR)with high band intensities and peaks under visible spectrum. A strong resonance at 540 nm is clearly seen in The UV visible spectroscopy of the synthesized nano particles were in the range of 400–800 nm. The plant extract showed to synthesize the gold nanoparticles by the indication of suitable surface Plasmon resonance (SPR)with high band intensities and peaks under visible spectrum. A strong resonance at 540 nm is clearly seen in Justiciaadhatodaand arises due to the excitation of surface plasmon vibrations in the gold nano particles.The average size of the nanoparticles is ~37 nm for AuNPs using Justiciaadhatodawith spherical and cubic shape. Among the four pathogens Klebsiella sp. andStapylococcus sp. Showed the maximum activity.