The diffusion coefficients of carbon in single and polycrystalline ZrC have been measured in the temperature range 1350°–2150°C, using radioactive tracer techniques. Volume and short‐circuit enhanced tracer diffusion coefficients are represented by the expressionsD*=1.32×102exp (−113 200/RT) cm2/sec andD*=1.6 exp (−90 000/RT) cm2/sec, respectively. The results are compared with apparent diffusion coefficients determined from existing carburization and high‐temperature creep data.