TiO2 particles, 30-300 nm in diameter, were prepared by thermal decomposition of titanium tetraisopropoxide (TTIP) using an aerosol microreactor, by which about 1 μl of the liquid precursor is injected into an evaporator, 1 cc in volume, and vaporized precursor is then transported by nitrogen as a bolus to a tubular reactor 4 mm in diameter and 35 cm in length. Investigated were the effects of the reactor temperature and the concentration of TTIP vapor on the morphology, particle size distribution and crystalline structure of produced TiO2 particles. With TTIP vapor concentration kept constant at 1 mol％, the reactor temperature was varied from 300 to 500 and 700 ℃. The primary particle size decreased with increasing the temperature, and the size distributions were mono-modal at 300 and 500 ℃, but bi-modal at 700 ℃. The TTIP vapor concentration was increased from 1 to 3.5 and 7 mol％, holding the reactor temperature at 700 ℃. The bi-modal distribution seen at the concentration of 1 mol％ disappeared and the number of particles composing an agglomerate increased at the higher concentrations. These effects of the reactor temperature and the precursor concentration were discussed in comparison with experimental results reported earlier.