An investigation has been carried out on the slow crack growth behaviour-of an advanced Si3N4 ceramic material at room temperature at different loading frequencies. The results clearly show a detrimental effect of cyclic loading on crack growth rate in terms of time and a reduced crack growth resistance with increasing cyclic frequency. Crack growth rates can be described by the Paris power-raw expression for both static and cyclic loading, but the exponent n increases with decreasing loading frequency. Further support for the existence of mechanical fatigue in this material is provided from experiments involving alternate cyclic and static fatigue using the same specimen, which show substantial differences in crack growth rate in terms of time. Removal of crack wakes resulted in an unchanged crack growth rate under sustained load, which suggests that the crack wake does not play a key role in enhanced crack growth under cyclic loading. The likely crack growth mechanism is discussed.