The modification of carbide characteristics through grain boundary serration and its subsequent effect on the creep-fatigue property at 873 K have been investigated, using an AISI 304 stainless steel. It was found that the grain boundaries are considerably serrated when a specimen is furnace-cooled. The grain boundary serration leads to a change in the carbide characteristics as well as grain boundary configuration, i.e., morphology of carbide from an acute triangular to a planar form and a lowered density. Additionally, an array of carbide particles is changed from a consistent to zigzag pattern, in terms of their preference to one grain to share the coherency. Planar carbides on serrated grain boundaries have a lower interfacial energy than that of triangular carbides on straight grain boundaries. It is suggested that the modification of carbide characteristics through the grain boundary serration has a remarkable influence on the improvement of creep-fatigue resistance. (C) 2003 Kluwer Academic Publishers.