Abstract: After an earthquake, has the strain energy in the rupture zone been fully released? Will there be another earthquake with similar magnitude occurring on the same fracture surface? These questions are important issues concerning earthquake doublets.In this paper we relocated the 2003 Dayao two earthquake sequences with doubledifference location algorithm (HypoDD), and found that the aftershock zones have expanded, but the two aftershock zones hardly overlap in both depth direction and horizontal direction. The DD relocation result also shows that the July 21 mainshock is to the northwest of the October 16 mainshock. In addition, P-wave polarization analysis result indicates that the fault plane strikes of the two mainshocks deviate slightly from each other. This is consistent with the situation of aftershock zone stretching. These results imply that the two Dayao earthquakes, which are near enough, may have occurred in different segments of a fault system. It can be assumed that these two rupture zones are not overlapped.