Polyesters are biodegradable analogues of polypeptides, but their biochemical applications have been hampered by the lack of a method to analyze polyester conformation in a solution state. We have demonstrated that vibrational circular dichroism (VCD) spectroscopy can conveniently and accurately elucidate the conformation of polyesters through the studies on poly(L-lactic acid) (PLLA), PLLA-amylose complex, and oligo(L-lactic acid). The analysis of VCD exciton couplet of these molecules has clarified the stable left-handed helical structure of PLLA, while density functional theory calculations of oligo(L-lactic acid) have revealed its detailed structural nature.