The spores of the Drynaria roosii Nakaike were cultured in inorganic medium and soil respectively. The spore germination and the gametophyte development were observed by microscope. The results indicate that the spores are yellowish, monolete, without perispore and bearing granular ornamentation on the exospore. They are bean-shaped in equatorial view and elliptical in polar view. The spores germinate within 10~12 days after inoculation, the type of germination is Vittaria-type while that of gametophyte development is Drynaria-type. The prothallial plates form in 20 days after inoculation and the establishment of apical cell is later than that. After the formation of the prothallial plate, profuse unicellular hairs occur on both the surfaces and margin of the prothalli. The young prothalli develop in 60 days after inoculation and the mature prothalli are cordate-thalloid. The sex organs are formed in 65 days after inoculation. The antheridia appear about 10 days earlier than archegonia. Archegonial neck usually inclines or curves towards the base of the prothallus at maturity. It can be observed that the embryos break through the archegonia after fertilization.