Thick films of Y3Al5O12:Eu3+ were dip-coated on silica substrate from sols. The synthesis was accomplished by using aluminium tri-sec-butoxide, yttrium chloride and europium nitrate as starting materials and isopropanol as solvent. Single-crystalline Y3Al5O12:Eu3+ cubic perovskite thick films were analyzed by X-Ray Diffraction and confirmed by Atomic Force Microscopy observations. The Y3Al5O12:Eu3+ thick film waveguiding properties was studied using an He-Ne laser (632.8 nm) for “m-lines” spectroscopy (MLS), which showed that film thickness and refractive index were 1.3 µm and 1.6385 0.001, respectively, after 1100 °C heat treatment. The increase is associated with film crystallization produced by different heat treatments.