[en] When poly-γ-methyl-L-glutamate (PMLG) fibers were irradiated with γ-ray from ⁶⁰Co, the strength-elongation and the molecular weight of the fibers decreased exponentially with the increase of radiation dose, and the Young's modulus gradually decreased. When the microstructure was examined by X-ray diffraction photographs, the crystals in the PMLG fibers were found to be little affected by γ-ray. Therefore, it was considered that the region affected by γ-ray might be the non-crystal region, and the reduction of the molecular weight by γ-ray was due to the breakage of the non-crystal region. The difference scanning calorimeter (DSC) curve for the PMLG fibers showed an absorption peak at 300 - 350 deg C, which was due to the melting and decomposition of PMLG. With the increase in radiation dose, this peak became broader, and the position of the peak was transferred toward lower temperature. It was considered that this phenomenon was due to the increase of severance of the non-crystal molecular chains, and the state of cohesion of the micro-crystals in crystal region weakened. The amount of heat absorption accompanying the melting and decomposition of PMLG gradually decreased with the increase of radiation dose. This fact also suggests that the state of cohesion of the microcrystals was weakened by the increase of radiation dose. (Kaihara, S.)