Based on the quarter-wavelength approximation by Boore and Joyner (1997), the frequent-dependent site amplifications at 87 free-field strong-motion stations in central Taiwan from borehole data are evaluated. Results show that the amplifications increase with frequency, and the amplification is larger at the sites in the Western Plain with Holocene alluvium than at those in the Western Foothill with Pleistocene and Miocene formations.