A process for synthesizing nano-sized rutile, anatase, or a mixture of rutile and anatase TiO2 powder. The process includes the steps of: 1) forming a Ti-peroxo complex by mixing H2O2 with a Ti compound, and 2) heating the Ti-peroxo complex at a temperature of above 50° C. A primary particle size of TiO2 particles, synthesized by the method, is below 50 nm, and an agglomerated particle size thereof after a washing/dry process is below about 10 μm. The major characteristics of the present invention are that it is a low temperature process, a highly concentrated synthesis, and high production yield of above 90%.