In order to investigate the effects of creep temperatures on the precipitation of S’ phases of Al-Cu-Mg alloys, the creep properties were measured at 125, 150, 175 and 200 oC and the difference of microstructure between the grip and the fracture area was observed through transmission electron microscopy (TEM). The results show that the length and thickness of S’ phases in the fracture area is twice as many as the grip area in the alloy crept at 150 oC under the stress of 345 MPa for 96 h. Compared with their grip areas, the length of S’ phases in the fracture areas of the sample crept at 175 oC under the stress of 265 MPa for 100 h and the sample crept at 200 oC under the stress of 210 MPa for 115 h is increased apparently, while the thickness is decreased slightly