The crystalline fraction of gamma-irradiated semicrystalline iron polymethacrylate was determined by X-ray diffraction analysis. In particular, the changes in the crystallinity index (CI) of the polymer as a function of the received dose (10-95 kGy) were studied and correlated with the parameters obtained by Mossbauer spectroscopy. We also analyzed the thermal degradation of the iron polymethacrylate in a sample with a maximum of crystallinity by employing the thermoanalytical techniques TGA and DSC.