In this work, nanomaterials and rare earths were obtained with application in the degradation of dyes since in the developing countries the decontamination of water bodies is essential. We used TiO2 for incorporation of rare earths applied to photocatalytic activity in degradation of methyl blue due to its high chemical stability and corrosion resistance. We obtain nanostructured materials of TiO2, TiO2: Ln3+ (Ln3+ = Sm3+, Gd3+ and Yb3+) by sol gel method, for decontamination of dye such as methylene blue in surface water bodies. Through x-ray diffraction, we found that anatase-rutile phase was achieved in TiO2 and tetragonal anatase phase in TiO2 : Ln3+. Size average in nanometres of 31, 37, 44 y 34 for TiO2, TiO2 : Sm3+, TiO2: Gd3+ and TiO2:Yb3+ respectively determinate by atomic force microscopy and by UV spectroscopy the energy gap (2.94, 2.87, 2.85 and 2.95) eV respectively. As for the degradation of the methylene blue dye, the best catalyst under UV radiation was TiO2 : Gd3+ with 54% degradation compared to TiO2 that presented 52%, 29% for TiO2 : Sm3+ and with 27% to TiO2 : Yb3+ determined by fluorimetry. These materials must be applied in industrial post-treatment processes using photo catalysis for the decontamination of bodies of water.