Formosan Rhododendron (Rhododendron formosanum Hemsl) is an endemic species of Ericales in Taiwan. In this study, ericoid endophyte was isolated from roots of Formosana azalea, and its ITS1-F-5.8S-TW13 sequence was compared with known ericoid endophytes from GenBank and identified as Cryptosporiopsis sp. This study also marked the new record of endophyte of Dermateaceae, Cryptosporiopsis of Ascomycetes in Taiwan. In mycorrhizal synthesis, the inoculated Formosana azalea seedlings grew well, and the ultrastructure showed that there were hyphal complex and hyphal coils in its cortical cells. These results demonstrated that Formosan azalea could form ericoid mycorrhiza in vitro with Cryptosporiopsis sp.