In relation to denaturation of proteins, thermo-induced conformational change of poly(D-glutamic acid) (PGA) was studied in the presence of poly (vinyl alcohol) (PVA) in the helix-coil transition region. The α-helix content decreased with annealing time in solution: only a helix-to-coil transition, being independent of the PVA content. The α-to-β₂ transition occurred during casting the mixed solution due to the intermolecular hydrogen bonding in the helio-to-coil transition region.