Ultra-fine titanium dioxide powders were synthesized by a thermal plasma processing. The phase compositions of powders are strongly influenced by reacting and collecting positions and the injecting method of TiCl4. Using a micro pump for injecting TiCl4, rutile contents in the powders collected for A-type reactor increases up to 95%. The powders collected at the other positions are found to be anatase of above 80% and most of the powders are spherical. The average sizes of powders are found to be below 100 nm at lower flow rate of TiCl4 than 1.0 g/min, but they rapidly increase at now rates of TiCl4 higher than 1.5 g/min, Using Ar-carrier gas for injecting TiCl4, the rutile content in powders increase to 60% with the flow rate of Ar-carrier gas. The average sizes of these powders are 30 nm, regardless of flow rate of Ar-carrier gas and collecting positions. The anatase-to-rutile transformation of produced powder starts at approx. 600 degreesC and finishes at below 1000 degreesC.