The effect of 60Co γ-radiation on the thermal conductivity of polypropylene (PP) has been studied over the temperature range 0–160°C. for radiation doses of 600 and 1800 Mrad. The conductivity of unirradiated specimens rises from 4.5 × 10−4 cgs units (cal./cm.-sec.-°C.) at 0°C. to 4.8 × 10−4cgs units at 80°C. and subsequently decreases with temperature to a value of about 3.1 × 10−4cgs units at 160°C. Upon irradiation to 600 Mrad the thermal conductivity is lowered over the 0–150°C. temperature range. Above 90°C. the conductivity decreases with temperature and becomes relatively constant at 3.4 × 10−4 cgs units from 120 to 160°C. Differential scanning calorimeter (DCS) measurements from 30 to 200°C. show that irradiation to 600 Mrad lowers the energy associated with crystalline melting and shifts the endotherm melting peak from about 160 to 105°C. Irradiation to 1800 Mrad results in additional lowering of the thermal conductivity over the 50–160°C. range, a further decrease in area of the endothermic peak and a shift of its maximum peak position to about 75°C. The effects of radiation on the thermal conductivity of polypropylene are compared and correlated with the observed effects of radiation on the dynamic mechanical behavior.