The diffusion coefficient for plutonium diffusing in isotropic pyrolytic carbon has been determined as a function of temperature. The apparent diffusion coefficient can be expressed by the equation D = 4.47 × 10’−8 exp(−55 0001R T) m2· s−1over the temperature range from 1273 to 2073 K. Evaluation and comparison of the plutonium diffusion data with that of uranium and thorium using a compensation law treatment resulted in a reasonably good correlation, thus implying similar diffusion mechanisms.