we interpreted high-resolution and multichannel profiles in conjuction with sea floor images and sediment cores to investigate the occurrence of shallow gas in the southern Ulleung Basin in the East Sea. Acoustic anomalies and gas seepages are revealed on sea floor images and seismic profiles. Gas samples from cored sediment consist entirely of methane. These features indicate wide occurrence of methane gas in sediments. The slope area at southern margin of the Ulleung Basin is characterized by deformed structure associated with expansion of gas. The slope base of the Oki Bank shows various acoustic anomalies created by gas such as acoustic turbidity, acoustic void, and mounds. Locally, the top of acoustic turbidity forms a bottom simulating reflector with reversed polarity on seismic profiles. We suggest that the occurrence of highly concentrated gas caused the secondary structural deformation of sediments.