The spherical particles of $CeO_2/SiO_2$ composite powder with narrow-size distribution and pure phase particles were synthesized by ultrasonic spray pyrolysis method from aqueous cerium sulfate solution. The resulting composite powder was characterized by X-ray diffraction, scanning electron microscopy, transmittance electron microscopy, in-vitro sun protect factor, and BET surface area analysis. The concentration of cerium sulfate was tested to vary the particle size from $3.40{ imes}10^{-3}$ to $1.02{ imes}10^{-2}mol/cm^3$ to study concentration effect of starting material. The average particle size from the $3.40{ imes}10^{-3}mol/cm^3$ concentration was found to be slightly smaller than that from the $1.02{ imes}10^{-2}mol/cm^3$ concentration, because of the relation between the droplet size and the concentration of the starting material solution