Juncus L. (Juncaceae) is a genus of annual and perennial herbs composed of approximately 310 species distributed worldwide, but more rarely found in the tropics. Despite an increasing number of karyological studies in Juncaceae, reports on chromosome numbers in Korean Juncus taxa have been scarce owing to the small chromosome size. Here, we present detailed information on chromosome numbers obtained from 36 individuals of 10 Korean Juncus taxa. Chromosome numbers of eight taxa (J. diastrophanthus, J. prismatocarpus subsp. leschenaultii, J. krameri, J. papillosus, J. wallichianus, J. gracillimus, J. fauriei, and J. setchuensis) are reported for the first time. All studied taxa have different chromosome numbers and ploidy variations (2n=30, 60, and 80) with small chromosomes. These ploidy level variations are of no systematic relevance in Korean Juncus taxa; however, this variation in chromosome number might provide additional evidence for the importance of morphological diversification via polyploidization including both auto- and allopolyploidization.