Using a premixed flat flame aerosol reactor, the experimental study on the morphological evolution of the aggregates was done. With the objectives to understand the morphological process of SiO2 and TiO2 particle that matches to the cases of the reaction-limited aggregation process and the diffusion-limited aggregation process respectively, the difference in chemical reaction rate of SiCl4 and TiCl4 was utilized under given flame temperatures. To evaluate the morphological evolution of the aggregates, the light scattering measurement and electron microscopy coupled with thermophoretic sampling method were used. In the case of SiCl4 oxidation that produces SiO2 particles, the microscopic observation obtained with respect to the axial position in the reactor showed that the diffusion-limited aggregation was the dominant mechanism in the aggregation process because that the very low reaction rates was maintained excepted the earlier reaction stage in the given reactor temperature profile. In the case of TiCl4 that maintains the higher reaction rate during the later reaction stage, it was observed that the reaction-limited aggregation process is the main mechanism on the aggregation. According to the results of the light scattering measurements, the fractal dimension of SiO2 and TiO2 aggregates was 1.23-1.84 and 2.81-2.94 respectively, and those results are corresponds with the photometric measurement. To observe applicability of TiO2 particles as photocatalyst, XRD analysis was conducted. TiO2 particles were generated in our study consisted of anatase mainly that has high photochemical activity.