Poly(l-lactic acid)-TiO2 nanocomposite films were prepared by twin-screw mixer and compression molding. Compatibility between polymer matrix and nanoparticles were improved by modification of the TiO2 surface with fluorocarbons plasma treatment. 2 and 5 were the % in weight of modified functionalized TiO2 (fTi) used in this work. Not modified TiO2 nanoparticles were also used at the same % for comparison. The nanocomposites were analyzed in terms of molecular mass, structure, morphology, thermal stability, mechanical properties and UV absorbance. It was found that TiO2 nanoparticles affected slighly the PLA molecular weight during mixing and the phenomenon was more marked for functionalized nanoparticles (fTi). All the films presented a good dispersion of nanoparticles in PLA matrix. However, a better interfacial interaction was found for nanocomposites containing modified nanoparticles, and this was reflected in the improved mechanical properties. Moreover, all the nanocomposites showed extension of UV absorption area and increase of the thermal stability. Both UV adsorption and thermal stability increased by increasing TiO2 content and at a given composition for nanocomposites containing modified TiO2.