Horsehair or gordian worms (Nematomorpha) were identified with 22 genera (Gordiida) and 5 marine species (Nectonema) until now. During juvenile phase in development, they gain parasitic activity in arthropods. In this study, a gordian worm was detected in the feces of a dog living in Nonsan-si, Chungcheongnam-do, Korea. Using this worm, we evaluated the morphological characteristics by light microscopic analysis. Furthermore, the morphological classification was re-evaluated by scanning and transverse electron microscopes. The worm was determined that it is male adult having a bi-lobed tail and male gonads in cross sections. Based on the morphological characteristics including cross sections of body and areole on the cuticle, the parasite was also identified as Gordius sp. (Nematomorpha: Gordiidae).