$TiO_2$ nanopowder was successfully prepared using a titanium tetra-isopropoxide. Subsequently, the effect of pH on the characteristics of the prepared $TiO_2$ nanopowder was evaluated depending on the amounts of the catalysts such as HCI and NH40H. The morphology and phase transformation of $TiO_2$ powder prepared by hydrolysis of titanium tetraisopropoxide were strongly influenced by the presence of the catalysts. In the case of using $NH_4$OH, the morphology of the $TiO_2$ powder exhibited powder form. For the HCI catalyst, it showed bulk or granule form. The phase transformations of amorphous $Ti(OH)_4$ to anatase $TiO_2$ and the anatase to rutile was significantly influenced by the kind and amount of the catalysts.