A model capable of representing the evolution rate of various damage mechanisms pertinent to creep rupture of austenitic stainless steels is utilized to study the role of grain boundary sliding on the damage evolution in the form of cavitational damage at grain boundary facets and wedge cracking at triple lines and on the creep lifetime of a standard creep specimen. Reduced grain boundary sliding reduces the rate of damage evolution and hence prolongs creep lifetime at higher stresses. However, creep lifetime at lower stresses is controlled by diffusional cavitation and remains unaffected by grain boundary sliding.