The competition between hydrolysis and oxidation of TiCl4 during vapor-phase synthesis of titania powders was experimentally investigated. The effects of reactor temperature, reactant mixing and H2O/TiCl4 ratio were studied in a hot wall aerosol flow reactor. The presence of water vapor resulted in rounded particles instead of the faceted ones observed in the absence of water; this effect was most pronounced at lower reactor temperatures. Mixing the water and TiCl4 vapor streams at low temperature resulted in anatase titania. Larger aggregates with smaller primary particles were observed for powders synthesized in the presence of water vapor. The mixing temperature of the water and TiCl4 vapors, as well as the H2O/TiCl4 ratios, did not affect the aggregate size or specific surface area. Analysis of micrographs of titania aggregates made in the presence of water revealed that the fractal dimension increased with process temperature.