The radiation decomposition of meta-terphenyl by 1.35-MeV electrons has been measured for temperatures from 200 to 440°C, beam currents from 3 to 100μA and average dose rates from 0.25 to 15 W/g. G(-terphenyl) was 0.25 at 300°C. Decomposition increased above 350°C and depended on the local radiation intensity rather than the average dose rate. At 440°C, G(-terphenyl) increased from 0.62 at 100-μA beam current to 1.6 at 3 μA. Decomposition increased with pulse frequency for intermittent irradiation. Postirradiation thermal decomposition was measured. Thermally initiated reactions did not contribute appreciably to decomposition during irradiation. The results indicate that above ≈ 350°C the radiolytic decomposition mechanism differs from that at lower temperatures. The data provide information about the contributions of radiolytic and pyrolytic decomposition in high-temperature organic-cooled nuclear reactor systems.