Abstract: A series of poly(ε-caprolactone-co-1,2-propylene glycol oxalate) (PCL-co-PPOx) copolymers were synthesized via bulk ring-opening copolymerization of ε-caprolactone (CL) with cyclic 1,2-propylene glycol oxalate (1,2-POx) as a modifying monomer. The polymerization behavior, physicochemical properties, mechanical properties, and degradation performance of PCL-co-PPOx were systematically investigated. Results demonstrated that the monomer conversion exceeded 94%, the number-average molecular weight (Mn,SEC) reached up to 131.5 kDa, and the crystallinity was determined to be 39.0%. The copolymer exhibited favorable mechanical properties with a tensile strength of 26.9 MPa and an elongation at break of 1928%, as well as excellent degradability, showing a weight loss of 66% after 28 days of degradation. This strategy provides an effective route for designing aliphatic polyesters with superior mechanical performance and tunable degradability.