EC1 is a subsurface mooring that has been deployed in the Ulleung Interplain Gap (UIG) since 1996. The UIG is the only deep channel connecting the northern Japan Basin and the southwestern Ulleung Basin in the East Sea (Japan Sea). The EC1 provides continuous time series data at depths ranging from 150 to 2,250 meters, enabling scientific research on circulation and water properties. It equips current-meter, conductivity, temperature, pressure, and dissolved oxygen sensors. The EC1 mooring was recovered 3 times (26 times total) and redeployed 3 times (26 times total) from November 2020 to April 2023 (since 1996), with a typical turnover time of 1 year. The equipment has been upgraded since 1996 to continuously measure temperature, pressure, conductivity, dissolved oxygen, and the speed and direction of three-dimensional current, as well as to collect more and better time series data. The sampling intervals of all sensors are equal to or less than 60 minutes. The temperature, pressure, conductivity, and dissolved oxygen data collected from November 2020 to April 2023 were quality-assured and quality-controlled with typical procedures such as global and local range tests, spike tests, and gradient tests. The magnetic declination of 9 degrees west was applied to the current data for compass calibration.