Serrated flow in a Ni-Co-Cr-base superalloy was studied in three microstructural conditions (SUB, SUBA, and SUPER) from 25 to 750 A degrees C by tensile test at initial strain rates ranging from 8 x 10(-5) to 3 x 10(-3) s(-1). The results showed that the SUB and SUBA samples had fine grain size of about 9 mu m, whereas the SUPER samples had coarse grain size of about 600 mu m. The tertiary gamma' fraction was about 0 in the SUB, 5% in the SUBA, and 15% in the SUPER samples, respectively. The types and temperature ranges of serration were different in the alloy with SUB, SUBA, and SUPER microstructures. It is proposed that the tertiary gamma' fraction and size had great effects on the serrated flow of the alloy with different microstructures.