Ultrafine SnO2 nanoparticles were successfully synthesized by microwave heating. Transmission electron microscopy images revealed that the size of primary particles of the synthesized SnO2 was around 5 nm. The SnO2 nanoparticles worked as a rechargeable electrode material, and the initial lithium insertion capacity of the SnO2 nanoparticles was 1670 mA h g(-1) which is significantly larger than that of a specimen synthesized by conventional method.