Six new species of copepods associated with polychaetes are described from Korea. Included are Indoclausia bipartita n. sp., Clausia parva n. sp., and Maxilliclausia propria n. gen. n. sp. in the Clausiidae; Pseudanthessius excertus n. sp. in the Pseudanthessiidae; and Polyankylis ovilaxa n. sp. and Sewelloya plana n. gen. n. sp. in the Polyankyliidae. The new genus Maxilliclausia has a peculiar maxilla in which the distal segment forms a sucking disk, a non-prehensile antenna, vestigial legs 3 and 5, and lacks a maxilliped and leg 4. The two new species of the Polyankyllidae are discovered as external associates of terebellid polychaetes. The new genus Sewelloya has a simple female maxilliped bearing only two small setae on its terminal segment, an uniramous leg 4 bearing 1-segmented exopod, and a reduced leg 5 represented by three setae. The genera Terebelliphilus Kim, 2001 which was originally placed in the Sabelliphilidae, and Octophiophora Stock, 1988 and Stockia Sebastian and Pillai, 1974, both of the latters with uncertain familial positions, are transferred to the Polyankyliidae. A key to five genera of the Polyankyliidae are provided.