Atmospheric Pressure Chemical Vapor Synthesis (APCVS) route was used for the synthesis of titania (TiO2) nanoparticles. The mechanism of nanoparticles formation were investigated by transmission electron microscopy (TEM), X-ray diffraction analysis, nitrogen adsorption technique (BET) and TG-DTA results for as-synthesized powders. The effect of precursor temperature, H2O effect and effective reaction (ER) zone temperature on the phase structure, nanoparticle size, agglomeration, coagulation, coalescence and nanoparticle morphology were also studied. Also, the effect of thermal velocity on the rate of powder formation, coagulation and coalescence of nanoparticles were discussed theoretically and experimentally. With introducing H2O, the appropriate rate of powder formation increased and size, coalescence and coagulation of nanoparticles decreased, significantly. Also, by using H2O vapor, the crystallinity of nanoparticles sharply increased. The minimum temperature for the synthesis of full anatase phase in atmospheric pressure was obtained to be 700 degrees C. With increasing precursor temperature, thermal velocity and the rate of powder formation increased. Also, no phase transformation was observed but size, coagulation, coalescence and agglomeration of titania nanoparticles increased whereas the morphology of nanoparticles was similar. (C) 2011 Elsevier B.V. All rights reserved.