Tin (IV) dioxide (SnO2) has attracted much attention due to its potential scientific significance and technological applications. SnO2 nanoparticles were prepared under low temperature and pressure conditions via precipitation from a 0.1 M SnCl4·5H2O solution by slowly adding NH4OH while rapidly stirring the solution. SnO2 nanoparticles were obtained from the reaction in the temperature range from 130 to 250˚C during 6 h. The microstructure and phase of the synthesized tin oxide particles were studied using XRD and TEM analyses. The average crystalline sizes of the synthesized SnO2 particles were from 5 to 20 nm and they had a narrow distribution. The average crystalline size of the synthesized particles increased as the reaction temperature increased. The crystalline size of the synthesized tin oxide particles decreased with increases in the pH value. The X-ray analysis showed that the synthesized particles were crystalline, and the SAED patterns also indicate that the synthesized SnO2 nanoparticles were crystalline. Furthermore, the morphology of the synthesized SnO2 nanoparticles was as a function of the reaction temperature. The effects of the synthesis parameters, such as the pH condition and reaction temperature, are also discussed.