We report on the fabrication and the structural study of TiO2/Er3+ planar optical waveguides. The effects of erbium concentration and annealing temperature were first studied using the waveguide Raman spectroscopy technique. The later showed an important modification of the TiO2 host matrix induced by the presence of the Er3+ ions. Depending on their concentration, these ions seem to stabilize the TiO2 amorphous phase or limit the crystallization process. This result is confirmed by transmission electron microscopy (TEM) and X-ray diffraction,