The surface diffusion of plutonium on uranium dioxide was measured in the temperature range from 1400 to 1830°C using a tracer method. A (U,Pu)O2 point source was placed and heated on the polished surface of a UO2 diffusion pellet. In the low-temperature range from 1400 to 1670°C, the product of the surface diffusion coefficient and high diffusivity surface layer, Ds · δ, was expressed by the equation As the temperature of diffusion anneal increases, the transport of some tracer atoms from the point source to the pellet surface appeared. In the temperature range from 1640 to 1830°C, the product, Ds · δ, was expressed by the equation