The effects of rejuvenation heat treatment (RHT) on the serrated flow behavior and fracture mode of nickel- based superalloys (R26) were investigated by tensile tests and microstructural characterization. The serrated flow activation energies were determined to be 41-72 and 64-81 kJ/mol before and after RHT, respectively. Dynamic strain aging in the alloy is caused by the diffusion of carbon atoms into dislocation channels in the nickel matrix. Before RHT, carbides are concentrated at the grain boundaries. Cracks initiate from these carbides and propagate along the grain boundaries. RHT dissolves carbides at grain boundaries, transferring crack initiation to the precipitated phase group in the grains. RHT increases carbon atom concentration in the nickel matrix, enhancing dynamic strain aging and serrated flow behavior.