To clarity the species of genus Melandrium (Caryophyllaceae) in Korea, the taxonomic characters were described and interspecific relationships were discussed to the extemal morphology with light and scanning electron microscopy. The position and size of appendages on petal, the shape and venation pattern of leaf, and the external morphology of seed and pollen were approved as the good characters to classify genus Melandrium in Korea. As the result, genus Melandrium in Korea could be arranged as 6 species, 1 variety, 1 forma. M. umbellatum was exclusively distributed in north Korea, and its taxonomic treatment was reserved.