The compression creep behaviour in air of pressureless sintered MgAl2O4-doped Si3N4 was studied at temperatures between 1473 and 1593 K, and under stresses between 50 and 300 M Pa. The variation of strain rate with stress and temperature was analysed to determine the stress exponent and the activation energy. Microstructural change was investigated by transmission electron microscopy. Up to 1533 K and 200 M Pa (low temperature, low stress) viscous creep (n ≃ 1) appeared as the predominant mechanism of deformation. At 1593 K and 200 to 300 M Pa (high temperature, high stress), extensive cavitation in intergranular vitreous phase produces the fracture of the samples. In the low-temperature region, strain whorls which are characteristic of grain-boundary sliding were observed at grain-boundaries in crept specimens.