Miniaturized electronic noses to rapidly detect and differentiate trace amount of chemical agents are extremely attractive. Use of tin oxide nanoparticles as sensing elements has been proved to significantly improve both the response time and the sensitivity of gas sensors or electronic noses. In this paper, we report the synthesis of pure tin oxide nanoparticles using a simple, convenient, and low-cost mini-arc plasma source. The nanoparticle size distribution is measured online using a scanning electrical mobility spectrometer (SEMS). The product nanoparticles are analyzed ex-situ by high resolution transmission electron microscopy (HRTEM) for morphology, crystal structure, and defects. Non-agglomerated rutile tin oxide (SnO2) nanoparticles as small as a few nm have been produced, with rounded shapes and some faceting on the lowest energy surfaces.