Sulfur-doped graphene quantum dots (S-GQDs) decorated with high-quantum-yield titanium dioxide (TiO2) nanocomposite are synthesized by a simple hydrothermal method. Photoluminescence characterization shows that S-GQDs exhibit stronger absorption peaks at ultraviolet (UV) region than GQDs. Photocatalytic activity of the obtained S-GQD/TiO2 nanocomposite reaches 70% in 8 min; this activity is significantly enhanced compared with those of GQDs/TiO2 and pure TiO2. Improved UV light absorption and effective transfer of photogenerated electrons can be attributed to integration of S-GQDs with TiO2 in a cladding manner. The present work provides a new approach for development of attractive GQD-based nanocomposites with controllable structures and photocatalytic performance.