Poly(ethylene adipate-co-L-lactic acid) (PLEA) copolymers were prepared via ring opening polymerization from L-lactide and hydroxyl terminated poly(ethylene adipate) prepolymer as starting materials. The composition and microstructure of the PLEA copolymers were characterized by nuclear magnetic resonance (H-1 NMR) spectra. Results confirmed the incorporation of lactic acid segments into the chain of PLEA copolymers as well as the existence of ester exchange reaction. The thermal behaviors and thermal stability of the resultant PLEA copolymers were evaluated by differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA), respectively; and the crystal structure was confirmed by using wide-angle X-ray diffraction (WAXD). Results showed that those properties of the PLEA copolymers showed high dependence on the composition of the copolymers.