Tin oxide (SnO2) nanoparticles were synthesized via a facile chemical precipitation route using tin chloride (SnCl2•2H2O) as precursor and ammonia as precipitant. The as-synthesized nanoparticles were subjected to post-calcination at 300°C, 400°C and 500°C and thoroughly characterized by advanced techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS) and Fourier transform infrared (FTIR) spectroscopy. XRD patterns revealed the formation of tetragonal SnO2 crystalline phase with average crystallite sizes of 11.9 nm, 13.9 nm and 17.2 nm for the samples calcined at 300°C, 400°C and 500°C respectively. SEM micrographs demonstrated agglomerated and irregular morphology of the calcined SnO2 nanoparticles. FTIR spectra confirmed the presence of characteristic Sn-O and O-Sn-O vibrational modes in the calcined SnO2 samples. The antibacterial activity of the synthesized nanoparticles was evaluated against model Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacterial strains by standard zone of inhibition assays. Remarkably, the SnO2 nanoparticles exhibited excellent antibacterial activity due to their high specific surface area. A systematic increase in the inhibition zone diameter was observed with decrease in crystallite size of SnO2 for both bacterial strains, suggesting an inverse relationship between crystallite size and antibacterial behavior. The present work demonstrates a simple, eco-friendly synthesis of antibacterial SnO2 nanoparticles with controlled crystallite size by tuning the calcination temperature.