The mechanism of low stress creep of uranium dioxide is identified as that modelled by Ashby and Verrall. This is supported by the agreements between predicter and experimental creep behaviours and creep rates. Evidence from the microstructures of superplastically deformed specimens confirms the topological aspect of the Ashby-Verrall model in these specimens. Superplastic strains of about 100% were obtained without failure of the specimens in a batch of 2um grain size specimens. The microstructures of these specimens revealed an even distribution of fine pores at triple point junctions. A mechanism is proposed to account for the superplastic behaviour of these specimens.