Four harpacticoid species belonging to the family Tachidiidae are reported from the coastal waters and salt marshes in South Korea: Tachidius discipes Giesbrecht, 1881, Neotachidius parvus Huys, Ohtsuka, Conroy-Dalton and Kikuchi, 2005, Microarthridion litospinatus Shen and Tai, 1973 and Geeopsis incisipes (Klie, 1913). The latter two species and genera are new to Korean fauna. The previous record of T. discipes reported by Song and Chang (1995) from Korea is affirmed by the finding of male specimens. Microarthridion litospinatus is first known outside the type locality, and redescribed herein in detail. A key to the five species and four genera of the family Tachidiidae hitherto known from South Korea is presented.