Abstract: IR and 2D-IR under variable temperatures (303 K to 393 K) were applied to the study of thermo-stability of crystalline and amorphous fractions of polyamide-66. As shown by the experimental results of testings by 1D-IR and 2nd derivative IR und variable temperatures, structures of the crystalline fraction of polyamide-66 were relatively sensitive to changes of temperatures, while structures of the amorphous fraction were relatively stable. And this phenomenon was further verified by the results of 2D-IR analysis. As observed from the molecular structure of polyamide-66, the crystalline fraction (relating mainly to O-C-NH-) was changed in advance with the raising of temperature of determination, while the structure of the amorphous fraction (relating mainly to -C-C-) was kept stable. It was shown by the results of asynchronous 2D-IR study, the absorption peaks of the structure of amorphous fraction were at 1 141 cm^-1 (ν_amorphous-1) and 1 138 cm^-1 (ν_amorphous-2), while for structure of crystalline fraction, the values were 939 cm^-1 (ν_crystal-1) and 931 cm^-1 (ν_crystal-2). The amorphous and crystalline fractions of polyamide-66 were further studied simultancously by synchronous 2D-IR, showing that the rate of change of the IR absorption peaks of the amorphous and crystalline fractions followed the order of 931 cm^-1 (ν_crystal-2) > 1 141 cm^-1 (ν_amorphous-1) > 939 cm^-1 (ν_crystal-1) > 1 138 cm^-1 (ν_amorphous-2).