Orchids are evolutionally known to be the most advanced plants in the order Liliales, and comprise approximately 1,000 genera and 35,000 species world-wide. In Korea, more than 110 species of Orchidaceae have been reported to be cultivated or to be collected in the wild. Orchids are mostly dependant on orchid mycorrhizae (OM) throughout or in part of their life cycle. The OM endomycorrhizae belonging to basidiomycetes or rarley ascomycetes are needed for orchid seed germination. Various fungi, including plant pathogenic, antagonistic and symbiotic fungi, were isolated from the roots of orchid native to Korea. The OM fungi collected from the roots of Cymbidium goeringii were three species of Rhizoctonia namely, R. repens (anamorph state of Tulsanella repens), R. endophytica (Ceratobasidium cornigerum), and an unidentified species (possibly an anamorph of T. calospora). These symbiotic fungi induced peloton in the cortical cells of orchid roots, and differed biologically and in 18s rDNA sequences from plant pathogenic Rhizoctonia species. Also, the mycorrhyzal fungi enhanced the orchid root absorption of nitrogen sources and minerals from the soil. The activity of mycorrhizal fungal hyphae in the roots caused prevention from pathogenic fungi. In nature, the peloton is observed in the cortical cells of Cymbidium goeriingii roots, indicating mycorrhizal colonization in the native orchid roots. On the other hand, pathogenic fungi such as Fusarium and/or Rhizoctonia species are mostly isolated from commercial orchid plants. These suggest that application of symbiotic mycorrhizal fungi should be needed for orchid cultivation in nurseries and at the time of transplanting.