The authors analyze co-seismic displacement field derived from the Global Position System (GPS) observations collected before and after the 2001 Kokoxili earthquake, western China.Using the co-seismic displacement data, and constrained with surface rupture data, they invert co-seismic slip distribution along the seismic fault. Their result shows that the earthquake ruptured the upper crust down to a depth of 13.1 ～ 22km (at 70% certainty), with its optimal estimate at 16.5km. A 2 ～ 3m left-lateral strike slip is resolved between the Sun Lake segment and the west end of the main rupture zone, although surface rupture has not been observed there. The surface rupture of this earthquake is ended at the Sun Lake to the west, but leftlateral slip of 1.5 ～ 2. 0m seems to exist beyond the east end of surface rupture observed from field geology. Seismic moment release estimated using GPS and surface rupture measurement is inversion.