To enhance the molecular weight and thermal stability of polyglycolic acid (PGA), low molecular weight PGA was modified through melt chain extension using epoxy chain extenders YMX-21 and YMX-48. Infrared spectroscopy analysis revealed the disappearance of characteristic epoxy peaks at 757 cm-1 and 910 cm-1, confirming that the epoxy groups of the chain extenders underwent ring-opening reactions with the terminal hydroxyl/carboxyl groups of PGA, achieving chain extension. Thermogravimetric analysis and differential scanning calorimetry characterization indicated that despite thermal degradation during processing, the chain extenders significantly improved the thermal stability of PGA, and this stability increased with the addition level; both chain extenders enhanced the intrinsic viscosity, with YMX-48 demonstrating superior chain extension efficiency. When the addition level of the chain extender was≤0.8% (mass fraction), the intrinsic viscosity decreased due to thermal degradation; however, when the addition level exceeded 0.8% (mass fraction), both systems exhibited a stable viscosity increase effect.