Among lignocelluloses, a component of wood, lignin is currently in the limelight as a green additive for imparting various functions such as reinforcing the mechanical strength of general-purpose plastics, antioxidation, and UV protection. In this study, lignin nanoparticles (LNPs) with a size of 100-200 nm were prepared using a gamma-valero-lactone-based solvent system. The prepared LNPs were added to poly vinyl alcohol (PVA), and PVA nanofibers incorporated into the LNPs were successfully prepared through electrospinning. The tensile strength of the PVA/LNPs nanofibers was improved by up to 338% as LNPs were added, and the morphology of the nanofibers was stably maintained without melting even when heat was applied at 200 °C, which is above the melting point of the matrix polymer. In addition, the added LNPs effectively prevented the degradation of PVA nanofibers by UV exposure. These results suggest that LNPs can be used as natural polymer additives that can provide effects such as thermal and mechanical stability and photolysis resistance to PVA nanofibers.