Nanosize titania colloidal solutions were prepared by the hydrolysis and condensation of titaniumtetraisopropoxide(TTIP) at room temperature. Hydrothermal treatment of this titania sol was carried out in an autoclave. As the H^+/TTIP mole ratio decreased and H₂O/TTIP mole ratio increased, stable sol was formed. The size and crystallinity remained unchanged after hydrothermal treatment of the stable sol at between 160 and 240℃. however, hydrothermal treatment of unstable sol produced rod-like particles and the crystallinity was changed from anatase to rutile.