Asia is a main distribution area of plants of genus Monochoria K. B. Presl, which often inhabit rice paddies, ditches and other wetlands. Among them, M. vaginalis (N. L. Burman) Kunth and M. korsakowii Regel et Maack are important rice paddy weeds. Like many other aquatic plants, species of the genus shows extremely morphological plasticity, which makes the delimitation of species unclear. To clarify the taxonomy and the variation of the genus Monochoria in Asia, large amount of herbarium specimens were studied, their natural populations in this area were intensively investigated, and the ontogenesis and morphological variations of the representative species from different locations were observed in detail in cultivation experiments. As a result of this study, genus Monochoria in Asia were revised, which were considered to contain five species and one variety, namely M. korsakowii, M. hastata, M. elata, M. valida, M. vaginalis var. vaginalis and M. vaginalis var. angustifolia. In addition, the paper briefly reviewed the taxonomic history of the genus, and evaluated the values of the main characters used in classification in a more objective way. The key to species of the genus, their morphological descriptions and geographical distributions were also presented.