Philonthus liopterus Sharp is reported for the first time in Korea. A habitus photo and illustration of the male genitalia of this species are provided. The genus Philonthus Stephens is a large group of the genera of subfamily Staphylininae with approximately 1,255 species worldwide (Herman, 2001) and characterized by the largest lateral macrosetal puncture of the pronotum separated from the lateral margin by little more than the width of the puncture. The apical maxillary palpomere is more or less fusiform,usually more than 1.3 times as long as the penultimate palpomere (Smetana, 1995). Philonthus samples were collected from Gangwon Province by Mr. Tripotin and identified as Philonthus liopterus Sharp, which is new to Korea. Including this species, a total of 33 species have been recorded in Korean Philonthus fauna. The diagnosis, habitus photo and illustrations of male genitalia of this species are reported. Philonthus liopterus Sharp, 1889: 36; Schillhammer, 1999:61; Herman, 2001: 2865; Smetana, 2004: 646. Philonthus kryzhanovskii Tichomirova, 1972: 1973 (treated as synonym of P. liopterus by Schillhammer, 1999). Philonthus kralianus Hromadka, 1987: 149 (treated as synonym of P. liopterus by Schillhammer, 1999). Korea: Gangwon Province: 1♂, Pyeongchang-gun, Jinbu-myeon, Mt. Odaesan near Dongdaesa, Alt. 800 m, 21 Jun-2 Aug 2006, 37°44'31''N, 128°35'71''E, ex ) Malaise trap, P. Tripotin coll.; 1♀, Pyeongchang-gun, Yongpyeong-myeon, Nodong-ri, Nodong Valley, Alt. 900 mm, 23 Jun-3 Aug 2006, 37°42'08''N, 128°28'89''E, ex ) Malaise trap, P. Tripotin coll. Body length 8.3-9.0 mm, body black but elytra reddish black, strongly glossy, antennae and legs reddish brown. Head suborbiculate, eyes slightly prominent, antenomeres 6-10 wider than long. Pronotum subquadrate but slightly narrowing posteriorly, dorsal rows each with four punctures. Elytra piceous black and sparsely punctuate. Medain lobe of aedeagus very elongate and apical area very sharp, paramere short and apical area very sharp like needle; middle area trapezoidal and dense sensory peg setae present underside. Korea, Japan, Russia, and Tajikistan. This species is identified easily from the other members of Korean Philonthus by strongly shining body and very sharp like needle of apex paramere.