A new draconematid nematode species of the genus Dinetia Decraemer and Gourbault, 1997 is described from the subtidal sediments and small logs from the eastern coast of South Korea. Dinetia orientalis n. sp. mainly differs from D. nycterobia Decraemer and Gourbault, 1997 by the following characters: large number of cephalic adhesion tubes (38–42 in male and 37–40 in female), number of posterior sublateral adhesion tubes (9–11 in male and 13–14 in female) and posterior subventral adhesion tubes (17–22 in male and 19–24 in female), the buccal cavity (narrow and armed with a dorsal and two weak ventrosublateral teeth), spicules (strongly arcuated and with a pair of strongly dilated gubernaculums around distal part of spicules), and higher “c” value (8.3–10.4 in male and 8.5–10.7 in female). This is the first report on free-living marine nematodes from South Korea, and the first record of the genus Dinetia in the Northwest Pacific.