The 1990-1997 annually surveyed GPS data form 36 stations and continuous data form 3 permanent stations in southwestern Taiwan are utilized to study the spatial and temporal variations of crustal strain in the area. Moderate to remarkable contraction rates of 0.48-2.01 m strain/yr in 91 degree- 135 degree are observed in the vicinity of the Chukou fault (CKF). The contraction rates decrease toward either the east or the west. Along the surface trace of the CKF, the strain rates of the northern segment are approximately at the same level, while that for the central and southern segments clearly increase toward the south. The temporal variations of crustal strain near the CKF are quite uniform during the period from 1990 to 1997. Analyzing the repeated GPS data of a dense profile across the central segment of the CKF from 1993 to 1997, it is found that the E-W shortening is distributed at several places and is not solely due to slip along the CKF. The east velocity components relative to Penghu increase dramatically form 2.6 mm/yr near the western coast to 39.9 mm/yr in the foothill region to the east of the CKF. These results indicate that crustal strain is accumulating rapidly and that there is a very high possibility of a forthcoming major earthquake in the Chianan area. The extremely high strain rates in the southern segment of the CKF may be caused by the aseismic slip on the fault as the seismic activity here is insignificant.