Cordyceps militaris specimens were continuously collected by Entomopathogenic Fungal Culture Collection (EFCC), Kangwon National University from different mountains, national parks and recreation parks of Korea from 1986 to 2002, mainly from late May to October of each year. Dry specimens of C. militaris along with their isolates have been preserved in EFCC. Fruiting of C. militaris was induced from single ascospore isolates as well as their combinations in brown rice medium. Fruiting experiments showed that combinations of single ascospore isolates produced fertile fruiting bodies, but single isolates could not produce any fruiting bodies. It was shown that two isolates of the opposite mating types were required to produce fertile stromata. However, combinations of the same mating type isolates produced no fruiting body, showing that C. militaris is a bipolar, heterothallic fungus.