The slabs of the second generation single crystal superalloy DD6 were cast using bi-seeded crystals with symmetric twist low angle grain boundaries. The influence of low angle boundary (LAB) on the stress rupture properties of the alloy was investigated at 760 oC/758 MPa, 850 oC/550 MPa and 980 oC/250 MPa. SEM was used to study the fracture surface and the failure mechanism. The results show that when the misorientation angle of LAB is relatively small it has a less effect on the stress rupture properties of the alloy. The stress rupture properties decrease with the misorientation increase on the same test conditions. The fracture characteristic of specimen shows intergranular rupture trend with the misorientation increases on the same conditions or with increasing of temperature and decreasing of stress for the same misorientation of LAB