Poor ultraviolet (UV) stability of polylactic acid (PLA) partially restricts its applications under atmospheric conditions. Titanium dioxide (TiO2) is a common and widely used UV-shielding agent, but detrimental effects often exists on the properties of polymers. In this study, we used polydopamine (PDA) to construct TiO2-PDA hybrid nanoparticles. The introduction of PDA can greatly reduce oxygen vacancies in TiO2, so as to better maintain the stability of the polymer matrix. TiO2-PDA hybrid nanoparticles were synthesized through simple steps and composited with PLA to prepare PLA/TiO2-PDA nanocomposites (noted as PLA/TP). The established PLA/TP films show excellent UV-shielding performance without sacrificing transparency (the transmittance at 550 nm is 85.7%). What's more, with 0.2 wt % nanoparticles added, the nanocomposite films have a good combination of strength and toughness. The performance improvement of PLA will broaden its application fields, making environmental materials have a wider range of uses and longer service life.