A draconematid nematode Prochaetosoma dokdoense sp. nov., first discovered in December 2006 at a subtidal zone of Dokdo, Korea, the northwest Pacific Ocean, is described. This new species was obtained from coarse detritus and shell gravels. Prochaetosoma dokdoense sp. nov. differs from all the species hitherto described by the following combination of characteristics: longer slender body (910-1175 µm), elongate loop-shaped amphidial fovea in male (distal end of ventral arm slightly curved anteriorly), eight cephalic adhesion tubes in both sexes positioned just anterior to swollen pharyngeal region, number of posterior sublateral adhesion tubes (6 in male and 6-10 in female) and posterior subventral adhesion tubes (7-8 in male and 8-9 in female), longer spicule length (78-86 µm), long cylindro-conoid tail (114-131 µm in male and 116-131 µm in female) and higher ratio c' (6.5-7.5 in male and 7.4-9 in female). A table comparing the major differential diagnostic characteristics of the species of the genus Prochaetosoma Micoletzky, 1922 is presented. For a reliable understanding of the geographic distribution and species identification of the genus Prochaetosoma, a pictorial key showing the relative length of non-annulated tail terminus to total tail length in both sexes is included, together with a dichotomous species identification key based on adults and fourth-stage juvenile as far as known. This is the first record of the genus Prochaetosoma in the northwest Pacific Ocean.