By using high-performance seismic sensors, dynamic characteristics of a base-isolated high-rise building and its change during construction are discussed. A series of ambient vibration data, several seismic response records and manpowered forced vibration data were obtained at the building in approximately one year of construction. Observed response characteristics, estimated natural periods, damping ratios and mode-shape are shown with the change of building height under the same isolator, soil and foundation condition. Difference of dynamic characteristics between seismic response and micro-tremor, and soil-structure-interaction effect are also discussed.