This study investigates the effects of plasticization and annealing on the thermal, dynamic mechanical, and rheological properties of poly(lactic acid) (PLA) using low molecular weight poly(ethylene glycol) (PEG) as a plasticizer. PLA/PEG blends were prepared with varying PEG contents (1–30 wt%) and analyzed using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and dynamic rheological measurements. The results show that PEG plasticization lowers the glass transition temperature (Tg) and cold crystallization temperature (Tcc) of PLA, while increasing crystallinity and crystallization rate. Blends with up to 20 wt% PEG were miscible, but phase separation occurred at 30 wt% PEG. Annealing at temperatures between 80–120 °C for 1–24 h increased crystallinity and favored the formation of a mixture of α' and α crystalline forms. The addition of PEG enhanced chain mobility, leading to improved crystallization and mechanical properties. The study also found that annealing increased the α to α' ratio, improving the heat deflection temperature and mechanical performance of PLA. The results highlight the importance of PEG content and annealing conditions in optimizing the crystalline structure and properties of PLA for industrial applications.This study investigates the effects of plasticization and annealing on the thermal, dynamic mechanical, and rheological properties of poly(lactic acid) (PLA) using low molecular weight poly(ethylene glycol) (PEG) as a plasticizer. PLA/PEG blends were prepared with varying PEG contents (1–30 wt%) and analyzed using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and dynamic rheological measurements. The results show that PEG plasticization lowers the glass transition temperature (Tg) and cold crystallization temperature (Tcc) of PLA, while increasing crystallinity and crystallization rate. Blends with up to 20 wt% PEG were miscible, but phase separation occurred at 30 wt% PEG. Annealing at temperatures between 80–120 °C for 1–24 h increased crystallinity and favored the formation of a mixture of α' and α crystalline forms. The addition of PEG enhanced chain mobility, leading to improved crystallization and mechanical properties. The study also found that annealing increased the α to α' ratio, improving the heat deflection temperature and mechanical performance of PLA. The results highlight the importance of PEG content and annealing conditions in optimizing the crystalline structure and properties of PLA for industrial applications.