Samples from sheets of the polymeric material Bayfol have been irradiated with X-rays, from a 50 kV X-ray tube, with different doses in the range 10-300 Gy. The resultant effect of X-ray irradiation on the thermal properties of Bayfol has been investigated using thermo-gravimetric analysis (TGA). The onset temperature of decomposition To and activation energy of thermal decomposition Ea were calculated, results indicating that the Byfol detector decomposes in one weight loss stage. The variation of transition temperatures with X-ray dose has been determined using differential thermal analysis (DTA). The results of the thermograms was characterized by the appearance of an endothermic peak due to melting. Melting temperature was found to be dependent on the X-ray dose. In addition, structural property studies using X-ray diffraction, infrared spectroscopy and intrinsic viscosity were performed on both non irradiated and all irradiated Bayfol samples. The results indicate that the degree of ordering, the absorbance, and the intrinsic viscosity of the Bayfol polymer are dependent on the X-ray doses.