In the present study synthesis of SnO2 nanoparticles have been carried out using Ocimum sanctum (O. sanctum) leaf extract as reducing agent via a microwave irradiation technique and studied their antibacterial properties. The SnO2 nanoparticles were used for antibacterial activity treatment by Agar disc diffusion method against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Proteus vulgaris, Klebsiella pneumonia, and Morganella morganii. Remarkable antibacterial activity has been observed by the SnO2 nanoparticles derived from O. sanctum extract due to the less nanoparticle size of SnO2 and essential phenolic compounds of O. sanctum leaves. The present investigation shows the mechanism for the reduction of SnO2 nanoparticles by the eugenol which is present in the extract of Ocimum leaves. Further, the powdered sample is characterized by Powder X-ray diffraction (PXRD), Scanning electron microscopy (SEM), UV-Vis spectroscopy, Fourier transform infrared spectroscopy (FTIR) and photoluminescence (PL) spectral analysis. In addition, the particle size of the SnO2 nanoparticles is calculated to be 20 +/- 2.5 nm from PXRD, broad absorption peak in the range of 200-450 nm from UV-Vis spectroscopy, and band gap of 3.75 eV from Tauc's plot. It is concluded that, the main focus of the study is cost-effective and eco-friendly green synthesis of tin oxide nanoparticles from the Ocimum leaf extract and study their properties.