In the present study, benthic diatoms from subtidal and tidal zones of Ulleungdo and Dokdo has been investigated. Sediment samples from six sites were collected from subtidal and tidal zones in November 2013 and August 2018, respectively. Hydrochloric acid and hydrogen peroxide were used to remove organic matter contained in the sediments, and permanent slides were prepared using naphrax resin. Total of 244 species belonging to 65 genera has been identified with observations under light microscope and scanning electron microsope. Two genera, 27 species and 3 subspecies were newly observed from Korean waters. About one third of the toal flora was epiphytic species. The Shannon-weaver index was high in the subtidal zone and low in the intertidal zone of Ulleungdo.