Acid catalyzed sol-forming reactions of titanium isopropoxide with water in isopropanol solutions were investigated by quasielastic light scattering (QELS) and viscosity measurements. Light scattering was used to determine the dependence of the intensity average mean diameter on time during the sol formation. The rate of increase of the specific viscosity was also determined. The rates of increase of diameter and specific viscosity exhibited similar complex dependencies on the HCl catalyst concentration; a minimum near 10 mM with a second decrease as the HCl concentration approached 100 mM. The dependence of these rates on the concentration of the acid catalyst was qualitatively similar to patterns observed for acid catalyzed sol formation by the reaction of silicon alkoxlides with water. The difference in the rates of increase of the colloid diameter and the specific viscosity was used to estimate the fractal dimension of the colloid during the sol formation. In the range of HCl concentration corresponding to a minimum in diameter growth rate, 5–20 mM for these solutions, the colloid species had fractal dimensions near 2. At acid concentrations increasing and decreasing from this range the fractal dimension increased to approach 3.