The Chi-Chi earthquake occurred in September 21, 1999, causing disastrous damages over wide areas in north-western part of Taiwan. Surface ruptures and seismic records showed particular and different motions in northern and southern part of Chelungpu fault. The origin of such unique behavior of Chelungpu fault promotes the Taiwan Chelungpu-fault Drilling Project (TCDP) started under the Taiwanese initiatives. TCDP thus provides a unique opportunity to observe and analyze the materials within the fault zone deeper than 1 km soon after a major earthquake. Characteristics of clay minerals within fault zone from TCDP may provide us helpful indicators to understand physical and chemical properties as well as the mechanism of earthquakes. This study collected the samples from the depth 600 m to 1300 m, especially focusing on the gouges in fault zones of the TCDP Hole-A. Two major fault zones (might be the Chelungpu fault zone) can be identified in depths 1111 m and 1153 m respectively, and here we report the discrepancy in clay minerals between those two major fault zones. The analyses of XRD show the dramatically characteristic variations in clay minerals: ① the smectite is rare or none in the most part of the 1111 fault zone but rich in the depth of 1111.29 m black material (more than 85%); ② the other clay minerals (illite, chlorite and kaolinite) are rich but decrease to zero in black zone of the 1111 fault zone; ③ the 1153 fault zone didn’t show a forementioned characteristics; ④ kaolinite is absent only in narrow depth of the 1111 fault zone, but absent in broad ones of the 1153 fault zone. Characteristics of clay mineralogy in the 1111 fault zone may be resulted from the devitrification of pseudotachylyte, occurred by the rapid slip of the seismic earthquake. It was consistent with the glass having been identified by TEM in the black layer of the 1111 fault zone, but not detected in the 1153 fault zone. The existence of pseudotachylyte indicate that the slip surface of seismic faulting event occurred in 1999 may be located in the depth 1111.29 m and the friction temperature may reach up to the 950℃. The Chi-Chi disease occurred in September 21, 1999, causing disastrous damages over wide areas in north-western part of Taiwan. Surface ruptures and seismic records pointed particular and different motions in northern and southern part of Chelungpu fault. The origin of such unique behavior of Chelungpu fault promotes the Taiwan Chelungpu-fault Drilling Project (TCDP) started under the Taiwanese initiatives. TCDP has provided a unique opportunity to observe and analyze the materials within the fault zone deeper than 1 km soon after a major earthquake. Characteristics of clay minerals within fault zone from TCDP may provide us helpful indicators to understand physical and chemical properties as well as the mechanism of earthquakes. This study collected the samples from the depth 600 m to 1300 m, especially focusing on the gouges in fault zones of the TCDP Hole-A. Two major fault zones (might be the Chelungpu fault zone) can be identified in depths 1111 m and 1153 m respectively, and h ere we report the discrepancy in clay minerals between those two major fault zones. The analyzes of XRD show the dramatic characteristic variations in clay minerals: ① the smectite is rare or none in the most part of the 1111 fault zone but rich in the depth of 1111.29 m black material (more than 85%); ② the other clay minerals (illite, chlorite and kaolinite) are rich but decrease to zero in black zone of the 1111 fault zone; ③ the 1153 fault zone did not show a foreback characteristics ; ④ kaolinite is absent only in narrow depth of the 1111 fault zone, but absent in broad ones of the 1153 fault zone. Characteristics of clay mineralogy in the 1111 fault zone may be resulted from the devitrification of pseudotachylyte, occurred by the rapid slip of the seismic earthquake. It was consistent with the glass having been identified by TEM in the black layer of the 1111 fault zone, but not detected in the 1153 fault zone. The existence of pseudotachylyte indicate that the sli p surface of seismic faulting event occurred in 1999 may be located in the depth 1111.29 m and the friction temperature may reach up to the 950 ° C.