© 2016 The Japan Society of Applied Physics. SnO 2 nanoparticles were successfully synthesized using a 900W microwave for 10, 20, and 30min. Tetragonal SnO 2 nanoparticles composed of Sn and O were detected by X-ray diffraction (XRD), selected area electron diffraction (SEAD), scanning electron microscopy (SEM), energydispersive X-ray (EDX) spectroscopy, and transmission electron microscopy (TEM). The SnO 2 nanoparticles processed for 30 min were the best crystals. The 3.5 eV energy gap and 395nm emission wavelength were determined by UV-visible absorption and photoluminescence (PL) spectroscopy. The gas-sensing performance of SnO 2 nanoparticles during exposure to an NH 3 -air mixture was studied at different working temperatures and NH 3 concentrations. At 1055 ppm NH 3 and 350 °C, the SnO 2 nanoparticles showed a sensitivity of 9.2 with the response and recovery times of 9 and 37 s, respectively.