Various insect pest damage agricultural crops and forest. Several control strategies have been tried against these pests. Using chemical pesticides is one of the major control strategies. However, in recent years, eco-friendly control measures have received a big attention. Entomogenous nematodes are best known as potential biocontrol agent which are promising alternatives of chemical pesticides. During the survey of insect-parasitic nematodes as well as their parasitism in Korea, three new species, Parasitylenchus cyrtogenii n. sp., Parasitylenchus oscavus n. sp., Bathymermis sancheongensis n. sp. and seven other new records for the Korean nematode and nematomorpha fauna were identified, which are: Howardula phyllotretae, Parasitaphelenchus uncinatus, Hexamermis albicans, Hexamermis sp., Heterorhabditidoides chongmingensis, Pristionchus pacificus, and Spinochordodea tellini, respectively. Parasitism of nematodes ranged from 0.7 to 87.5%. The highest parasitism was recorded in P. cyrtogenii n. sp isolated from Cyrtogenius brevior as 87.5%, however the lowest parasitism found in Hexamermis sp. isolated from Oxya chinensis as 0.7%.