Genus Ludwigia L. (Onagraceae Juss.) has 75 species, widespread distributed in tropical and subtropical regions of the world, on different kinds of soil. In Vietnam, the Ludwigia has 6 species. In this article, the authors described characteristics of genus Ludwigia in Vietnam, added information of distribution, habitat, ecology and use of this genus in Vietnam, and established diagnostic key to the 6 species of Ludwigia in flora of Vietnam.