Abstract: The effects of wall thickness on the high-temperature stress rupture properties and fracture behavior of DZ125 directionally solidified superalloy were studied using thin-walled specimens. The result shows that the stress rupture life of the thin-walled specimens is significantly shorter than that of standard ones, indicating there is significant thin-wall effect. There is an obvious linear relationship between wall thickness and stress rupture life. The edge zone of the fracture surface of thin-walled specimens was seriously oxidized, while the inside zone was microvoid coalescence fracture. The fracture of thin-walled specimens is the coalescence of the " surface oxidation-crack initiating-crack growth” and " inside creep damage”. The creep property of the alloy under 197 MPa/950 ℃ shows that the stress rupture life of round specimens is significantly higher than that of thin-walled ones. The stress rupture life of the thin-walled specimens with the wall thickness of 0.6 mm and 1.1 mm is nearly 50% and 80% that of round specimen, respectively.