Using a unique oblique angle co-deposition technique, well-aligned arrays of Ag nanoparticle embedded TiO2 composite nanorods have been fabricated with different concentrations of Ag. The structural, optical, and photocatalytic properties of the composite nanostructures are investigated using a variety of experimental techniques and compared with those of pure TiO2 nanorods fabricated similarly. Ag nanoparticles are formed in the composite nanorods, which increase the visible light absorbance due to localized surface plasmon resonance. The Ag concentrations and the annealing conditions are found to affect the size and the density of Ag nanoparticles and their optical properties. The Ag nanoparticle embedded TiO2 nanostructures exhibit enhanced photocatalytic activity compared to pure TiO2 under visible- or UV-light illumination. Ag plays different roles in assisting the photocatalysis with different light sources. Ag can be excited and can inject electrons to TiO2, working as an electron donor under visible light. While under UV illumination, Ag acts as an electron acceptor to trap the photogenerated electrons in TiO2. Due to the opposite electron transfer direction under UV and visible light, the presence of Ag may not result in a greater enhancement in the photocatalytic performance.