Abstract: Submarine canyons, a kind of elongated, narrow and deep negative reliefs, are common at active or passive continental margins. The Penghu submarine canyons are characterized by large slope and complex landform. High resolution single-channel 2-D seismic data are used in this paper to identify submarine canyons. Data shows that the canyons are generally in" V" shape or" U" shape, or "U" shape with a wide bottom in seismic profiles. Strong erosional features are commonly observed in the upper reaches of the canyons. There secondary grooves and slope gullies without sediment infilling are quite common. The formation of the Penghu submarine canyons is related to the sea level change during the late Quaternary. In the low water stage, the shelf was widely exposed to air and deposition occurred only in the area out of the shelf or even on the upper slope. Active gravity flow contributed to the formation of the submarine canyons.