Mylonchulus jinjuensis n. sp. is 1.8-2.2 mm long, spicules 58-$67{mu}textrm{m}$ long and is distinguishable by basally situated subventral teeth, presence of hypodermal glands and ventural body pores. Mylonchulus taeguensis n. sp. is 1.3-1.8 mm long, spicules 52-$64{mu}textrm{m}$ long and is characterized by having small denticle on dorsal wall of buccal cavity at the level of dorsal tooth apex, and two each pre- and post-vulval papillae. Mylonchulus polynicus is reported here for the first time from Korea, is described and illustrated. Princhulus pachydermis n. sp. is 2-2.3 mm long and is distinctive in having very thick body cuticle and absence of caudal glands and spinneret. Prionchulus koriensis n. sp. is 1.7-2.0 mm long and is characterized by having elongate-conoid tail with sharply pointed terminus and presence of caudal glands.