A degradable polymer was prepared from α-angelica lactone, a five-membered unsaturated lactone, by ring-opening polymerization (ROP). The polymerizability of α-angelica lactone was explained by a DFT calculation. The degradability of the resultant polymer and the reaction kinetics of α-angelica lactone ROP were also considered. Owing to the presence of a C
C bond in α-angelica lactone, the ROP of five-membered cyclic lactone becomes feasible under moderate conditions and the resultant polyester exhibits good degradability under light or acidic/basic circumstances. Since α-angelica lactone can be easily obtained from the commercially available green bio-platform chemical levulinic acid, its ROP may provide a potential route to produce functionalized aliphatic polyesters from renewable resources.