One plant seed extract (Psidium guajava) was screened for their bioreduction behavior for synthesis of silver nanoparticles. Psidium guajava (PG) was found to exhibit the good reducing and protecting action in terms of synthesis rate and monodispersity of the prepared silver nanoparticles. UV–visible spectroscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray energy dispersive spectrophotometer (EDAX) was performed to ascertain the formation of Ag-NPs. Our measurements indicate that biosynthesis of Ag nanoparticles by Psidium guajava (PG) produces Ag nanoparticles with the diameters in the range of 30-36 nm. XRD studies reveal a high degree of crystallinity and monophasic Ag nanoparticles of facecentered cubic (FCC) structure. The FTIR result clearly showed that the extracts containing OH as a functional group act in capping the nanoparticles synthesis. Antibacterial activities of Ag-NPs were tested against the growth of Gram-positive (S. aureus) using SEM. The inhibition was observed in the Ag-NPs against S. aureus. The results suggest that the synthesized Ag-NPs act as an effective antibacterial agent. It is confirmed that Ag-NPs are capable of rendering high antibacterial efficacy and hence has a great potential in the preparation of drugs used againstbacterial diseases. Manuscript profile