As a recent infrageneric classification of Juncus (Juncaceae), Kirschner suggested two subgenera which are distinguished by the type of inflorescence and the absence/presence of bracteole along with 10 sections which are distinguished by the characters of the leaves, the position of the inflorescence, and types of stamens and seeds. However, an intensive morphological investigation on Korean Juncus has yet to be performed. We surveyed the morphological characters of 14 taxa distributed throughout the Korean peninsula, including one North Korean taxon. The quantitative and qualitative characters of rhizomes, leaves, inflorescences, flowers, fruits, and seeds were investigated on each taxon using about 950 specimens of Korean Juncus on loan from major Korean herbaria. As a result, we provide diagnostic characters with illustrations and a key to Korean Juncus.