in this thesis, effects of surfactant composition and concentration on shape, size, zeta potential, and photocatalytic activity of tio2 nanosized particles are reported. spherical, cubic, rod, ellipse and leaf-like shaped tio2 nanosized particles were obtained with the addition of different surfactants in various composition and concentrations during preparation. the results show that the shape and size of the tio 2 nanosized particles depend on not only surfactant composition but also surfactant concentration. the ph dependence of zeta potential of tio2 nanosized particles was studied. a unique finding is that tio2 nanosized particles shaped by sodium dodecyl sulfate (sds) have two isoelectric points (ieps), while other shape-controlled tio2 nanosized particles have only one iep. at neutral ph, shape-and size-controlled tio2 nanosized particles have a more negative zeta potential than tio2 nanosized particles obtained without the addition of surfactants during synthesis and commercial anatase tio2 nanosized particles degussa p-25. different zeta potential values are observed for tio2 nanosized particles obtained with the addition of different surfactants during preparation. the addition of sds in tio2 nanoparticle suspensions causes a shift of the leps to lower ph values. photocatalytic activity of prepared tio2 nanosized particles was evaluated in fixed film batch reactors. tio2 nanosized particles with different shapes and sizes showed different activities in photocatalytic decomposition of methyl orange (mo) and phenol. photocatalytic activity of shape- and size-controlled tio2 nanosized particles is higher than those without the use of surfactant and p-25. photocatalytic decomposition of phenol and mo follows the first order reaction kinetics. the analysis of reaction rate constants and adsorption equilibrium constants shows that the shape is more important than the size in determining the photocatalytic activity of shape- and size-controlled tio2 nano sized particles. a comparison of the reaction rates indicated that tio2 nanorods have higher photocatalytic activities than spherical and cubic tio2 nanosized particles. all these results indicate that shape, size, zeta potential and photocatalytic activity of tio2 nanosized particles can be manipulated with the introduction of surfactants (types and concentrations) during preparation.