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Polysulfone Tecason S samples, designed for use in nuclear facilities, were aged under different conditions to simulate their long-term use in nuclear power plants. The specimens, with thicknesses of 4 mm, were irradiated with 60 Co g rays in oxygen and/or in air at different temperatures and thermally aged at 1808C. For all samples, the glass-transition temperature, the stepwise change in the heat capacity at the glass-transition temperature, and the oxidative induction temperature were measured with differential scanning calorimetry. Simultaneously, the mechanical properties were determined and correlated with the results obtained by differential scanning calorimetry. Although the material was aged under very harsh conditions (irradiation in oxygen with absorbed doses up to 500 kGy and thermal aging at 1808C up to 115 days), the detected changes were relatively small. Nevertheless, a tendency of the glass-transition temperature and oxidative induction temperature to decrease with advanced material degradation was evident. The color changes of the cross-sectional slices of some samples clearly indicated that the degradation was due to diffusion-limited oxidation not homogeneously distributed throughout the sample bulk. In addition, samples from the near surface layers and from the center of the sample were examined.