Blended films composed of poly[(R)-3-hydroxybutyric acid] (P3HB) and lignin wastes were prepared to adjust the mechanical and optical properties of P3HB films. In addition to the organosolv lignin extracted from oak, the oligomeric or polymeric byproducts obtained during the reductive catalytic depolymerization of lignin were mixed with P3HB. This adjusted the mechanical and optical properties of films to manipulate biodegradable P3HB films and create new applications of lignin wastes. When the solid residue obtained from depolymerization of organosolv lignin in an aqueous methanol solution was mixed with P3HB, the elongation at the break increased from 1.6±0.3% to 4.9±1.0% and Young’s modulus decreased from 1.97±0.21 GPa to 0.98±0.11 GPa depending on the depolymerization conditions. The films composed of P3HB and organosolv lignin blocked UV and a great deal of visible light, exhibiting 0.3–11.1% transmittance of UVA and 24.8–61.6% transmittance of visible light. However, those composed of P3HB and depolymerized lignin prepared during lignin depolymerization exhibited significant UV blocking with good transparency, featuring 0.7–39.8% transmittance of UVA and 33.7–78.3% transmittance of visible light. The adjusted mechanical and optical properties of blended films can be attributed to the interaction between P3HB and lignin derivatives. This study can be useful to valorize lignin-based waste obtained during the process of depolymerizing lignin to valuable phenolic monomers. Moreover, it can contribute to the development of the lignin-based sustainable chemical industry.