Bismuth-doped Tin Oxide (BTO) nano-particless were prepared by chemical co-precipitation method using SnCl4.5H2O and Bi(NO3)3.5H2O as precursors and NH3.H2O as precipitant. Effects of processing parameters on particle were investigated. These parameters include reaction temperature，terminal pH，doping bismuth content, calcine temperature, and PEG-600 dispersant. The BTO precursors were studied by TG-DTA. The product particles were characterized by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The optimized conditions for preparing nanometer BTO powders were proposed: reaction temperature of 60℃, terminal pH of 3, and the calcine temperature of 600℃, the minimum resistivity of BTO powders is 3.48Ω•cm under the optimized conditions.