In this work, we fabricated crystallite solid and porous TiO2 nanoparticles (NPs) using a surfactant-templated aerosol process. Specifically, Brij-58 surfactant was employed as a template in TiO2 matrix. The porosity of TiO2 NPs was controlled by varying the amount of Brij-58. The effect of TiO2 porosity on the photocatalytic reactivity was systematically examined. As a result, the highly porous TiO2 NPs exhibited much better photocatalytic reactivity than the low porosity TiO2 NPs. This suggests that the particle size, crystallite structure, and specific surface area play an important role in enhancing the photocatalytic reactivity of the TiO2 NPs.