The East Sea Current Measurement (EC1) is a subsurface mooring located in the deep channel of the Ulleung Interplain Gap (UIG) in the southwestern East Sea (Japan Sea), connecting the Japan Basin (JB) and Ulleung Basin (UB). The EC1 was first deployed at a depth of 2300 m in 1996 and has been operated to provide long time-series of currents and water properties. The UIG, a unique conduit for deep water exchange between JB and UB, is approximately 75 km wide and more than 2000 m deep, with a slight broadening towards the UB in the southwestern East Sea. Single point current-meters and other sensors are attached at 400 m, 1400 m, 2200 m, and other depths of the EC1 mooring. An upward-looking acoustic Doppler current profiler is often mounted between 100 and 500 m. In 2017, dissolved oxygen sensors were added at 1400 and 2250 m. The sampling intervals of the sensors are less than an hour. The data are quality controlled and quality assured before provision to the community via OceanSITES and SEANOE.