Near-inertial (~18 hours) internal waves were observed in the mid-western part of the East Sea on May 18 and 19, 2004 using C-band Synthetic Aperture Radar (SAR) images. Current and temperature measurements obtained during the field experiment from 10 May to 9 June 2004 (IWXES2004, Internal Wave eXperiment in the East Sea), were analyzed to investigate the processes by which near-inertial internal waves can be seen in SAR images and how they progress. The spatial distributions of horizontal wavelength and phase speed estimated from two successively acquired SAR images are consistent with those inferred from water temperature and current measurements carried out during the field experiment. Based on these two independent observations (SAR and IWXES2004), we report a strong possibility that the observed wave patterns in the SAR images during IWXES2004 are near-inertial internal waves propagating westward off the east coast of the Korean peninsula with a phase speed of about 0.3 m/s.