The high-temperature compressive creep behaviour of silicon nitride ceramics with different densification aids has been investigated. The microstructure of the as-received materials consists of randomly oriented rod-shaped beta-silicon nitride grains with no remaining (x phase. The grains have average dimensions of about 1.5 mum. length and 0.5 mum width. Creep experiments were conducted in an argon atmosphere at temperatures ranging from 1450degreesC to 1700degreesC and under stresses from 20 to 125 MPa. The stress exponent n and the activation energy Q were measured from stress and temperature changes. Values of n <1 and Q depending on increasing (&UDelta;T > 0) or decreasing (DeltaT < 0) temperature changes were found. Although no macroscopic failure was observed after relatively large strains (&SIM;30%), cavities developed along grain boundaries. The creep parameters may be consistent with a shear-thickening behaviour.