Poly(lactic acid)/sesbania gum/nano-TiO2 composites were prepared by melt blending in the mixing chamber of a torque rheometer in this work. The processing rheological properties, mechanical properties, morphologies, thermal properties, and optical properties of the resulting composites were evaluated. Effects of nano-TiO2 content and plasticizer content on the processing rheological properties and mechanical properties of composites were discussed. Scanning electron microscopy micrographs clearly revealed good dispersion of nano-TiO2 aggregates in the matrix at the low nano-TiO2 content, while higher content contributed to easy aggregation within the matrix, which was consistent with the results of mechanical properties, thermal properties, and optical properties. As for the processing rheological properties, a reasonable choice of nano-TiO2 and plasticizer content should be made depending on the used processing equipment and process.