Two large aftershocks of the 1999 Chi-Chi earthquake (ML= 6.4 and 6) occurred to the south of the Chelungpu fault and in the China-Yi in Taiwan. Near-field seismograms estimated some source parameters of the two events. The near-field seismograms estimated some source parameters of the two events. The near-field displacement spectra can be described by Brune's ω-square model. The estimated values of stress drop (Δσ), apparent stress (σa), and scaled energy (Es/Mo), of these two events varied from station to station with mean values of: Δσ= 991 bars, σa = 402 bars, and Es/Mo= 1.0 × 10-3 for the ML 6.4 event; and Δσ= 831 bars, σa = 337bars, and Es/Mo= 1.0 × 10-3 for the ML 6.0 one. This shows a high dynamic stress drop between these two events. The larger values calculated from the ML 6.4 event indicated a higher percentage transformation of strain energy into seismic-wave energy comparing to the ML 6.0 event.