There are many abandoned rice fields all over Japan. Most of them were abandoned by set-aside programs that began in 1970. This paper deals with the vegetation of wet abandoned rice fields in Hiroshima Prefecture. From the case study in the Saijo Basin, Higashi-Hiroshima, four plant communities are described : the Juncus leschenaultii community on the first-year fields, and three communities on older fields, the Ischaemum aristatum var. glaucum-Eupatorium lindleyanum community, the Isachne globosa community and the Eleocharis kuroguwai community. Vegetation change on abandoned rice fields is explained based on the species composition of abandoned rice fields communities and natural wetlands communities. Six threatened plant species were found on abandoned rice fields in Hiroshima Prefecture. Old abandoned rice fields have developed into various kinds of wetlands such as swamp woods, Moliniopsis marshes, sedge marshes and reedswamps. Although the old abandoned rice fields are the secondary wetlands, they will be more and more valuable in the future as the wildlife habitats not only in Hiroshima Prefecture but also in many other places in Japan.