An X-ray method for evaluating the α-form fraction of poly(γ-methyl glutamate) coexisting with the α-form crystal is described. The transformation from the α-helix structure to the β-pleated sheet structure in drawn specimens was found to be induced by annealing above a certain temperature in the presence of dichloroacetic acid. The transformation from the mixture of the α-and the β-forms to the β-form occurs slowly upon annealing at 423K and very rapidly at 453K for poly(γ-methyl glutamate) cast from a solution in dichloroacetic acid. The volume fraction of the β-form changed linearly with the logarithm of annealing time. The following factors were found to be essential for the completion of the α→β transformation: (1) the presence of dichloroacetic acid molecules which are thought to weaken the intramolecular hydrogen bond of the α-helix and facilitate the thermal molecular motion of the α-helix core, (2) a temperature high enough to provide the α-helix crystal with sufficient thermal energy, and (3) the presence of the β-form crystal as nuclei in the matrix of the α-crystal for the growth of the β-form crystal. The process conditions based on these factors were successfully applied for preparation of a high modulus fiber resembling to silk with respect to its modulus and crystal structure.