At the temperature range of 760 °C to 1100 °C, the transverse tensile properties of a nickel-based third generation single crystal superalloy were studied. The microstructures and fracture surfaces were observed by optical microscopy (OM), field emission scanning electron microscopy (FESEM) and scanning transmission electron microscopy (STEM). The results show that the tensile strength of the alloy decreases as the temperature increases, while the tensile elongation of the alloy increases with the temperature increasing. The fracture surfaces of the tensile ruptured specimens are characterized by quasi-cleavage features at 760 °C and 850 °C. At the temperature range of 980 °C to 1100 °C, dendrites characteristics exhibiting the solidification direction are observed on the fracture surfaces and the proportion of dendrites characteristic on the fracture surfaces increases with the temperature increasing. The fracture surface displays mixed quasi-cleavage and dimple features at 980 °C. The fracture surfaces are characterized by dimple features at 1070 °C and 1100 °C. As the temperature increases, more slip systems tend to be activated during the plastic deformation, result in different dislocation configurations. At 760 °C, high density a/2<110> dislocations are found to distribute roughly parallel with each other in the tensile ruptured specimens. The dislocations are observed to be tangled at 980 °C and dislocation networks have formed at 1100 °C.