The destruction of natural habitats of wild plant species is accelerating due to environmental changes and various human activities. This situation requires sustained and extensive efforts to preserve and safeguard wild species. The National Institute of Genetics (NIG), Mishima, Japan, maintains 1,701 accessions of 20 wild species of the genus Oryza, which have been collected from tropical and subtropical areas all over the world. This paper reviews the history, biodiversity, ex-situ conservation, and utility of the NIG wild Oryza collection. In addition, we describe our recent activities to improve the reliability of the collection and our contributions as part of the National BioResource Project (NBRP) of Japan. This project aims to provide reliable and high-quality rice materials for researchers worldwide. As part of the NBRP, we have evaluated wild Oryza accessions for eighteen morphological or physiological traits of vegetative and reproductive organs and for resistance to bacterial blight disease, developed molecular markers to distinguish species and/or genome-species in the genus, and published the information on the Oryzabase database.