Aliphatic polycarbonates (APCs) are an important class of biodegradable polymers with excellent physical and chemical properties and biocompatibility [1.-2].One of them, poly (octamethylene carbonate) (APC-8), demonstrates multi-level crystal transition and secondary crystallization behavior, as Figures 1 and 2.The reversible crystal transition between α and β form is very similar to the Brill transition of nylons[3-5].It is concluded that the reversible transition between the trans and gauche forms of the conformation of methylene sequences led to the multi-level crystal transition of APC-8.For the β form, the trans coexisted with the gauche forms, while for the δ form, the trans forms took the dominated position.