Formation behavior and photo-oxidation abilities of nanostructuredTiO2 powders were investigated through a direct crystallization from aqueousTiOCl2 solutions containing various metal chlorides at100 °C. Theobtained TiO2 powders without any additives and those withNi2+,Fe3+ and Nb5+ ions added, which have a similar positive ionic radius toTi4+, were mainly crystallized with rutile phase, whereas those withAl3+ and Zr4+ ions added, which have a quite different positive ionic radius, were mainlycrystallized with anatase phase. On the other hand, the secondary particles in theTiO2 powder consisted of acicular and spherical primary particles, corresponding to rutile andanatase phases, respectively. From these results, it seems that the positive ionicradius of the additives would affect phase formation as well as morphology ofTiO2 precipitates.Among the TiO2 powders prepared, Ni-added powder, which consisted mainly of rutile phase with a smallamount of anatase phase, showed excellent photocatalytic ability in decomposition of4-chlorophenol.