The nanocomposites were obtained from commercial multi-walled carbon nanotubes (MWCNTs) and with titanium tetra propoxide as TiO2 precursor, and heat treated at 400 degrees C and 500 degrees C to form crystalline phases of TiO2. The nanocomposites were investigated for their photocatalytic activity, employing them as catalysts in the degradation of organic methyl orange dye in an aqueous solution under UV radiation. The results were associated with the characteristics of the nanocomposite structure, using techniques such as x-ray diffraction, transmission electron microscopy, and Raman spectroscopy. Optical characterization was obtained by photoluminescence spectroscopy and diffuse reflectance spectroscopy. The highest photocatalytic efficiency was observed in the TiO2-MWCNT nanocomposites obtained in an acid medium and heat treated at 500 degrees C. These results could be associated with the lower transition energy and level of defects in the TiO2 of these nanocomposites when compared to the other samples.