Provided is an amorphous silica-titania composite oxide powder which has superior fluidability when being filled in a resin or the like upon use and has superior transparency compared with the existing silica-titania composite oxide particles. An amorphous silica-titania composite oxide powder which comprises amorphous silica-titania composite oxide particles that are not treated with a surface treating agent, wherein the content of particles each having a refractive index at a measurement wavelength of 589 nm of 1.46 or more, a volume-based cumulative 50% diameter of 0.1 to 2.0 μm and a particle diameter of 5.0 μm or more is 10 ppm or less, and the water absorption rate which is measured by drying the powder at 110℃ for 12 hours in the atmosphere and then storing the dried powder for 24 hours under the conditions including a temperature of 25℃ and a relative humidity of 85% to allow the powder to absorb moisture, and is calculated from the mass X of the powder before the absorption of water and the mass Y of the powder after the absorption of water in accordance with the formula: (Y-X)/X × 100 is 0.8% by mass or less. The amorphous silica-titania composite oxide powder is produced by exactly adjusting the silica coating conditions in the production of a silica-coated silica-titania composite oxide and burning silica-coated silica-titania composite oxide at 900℃ or higher.
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