Ferns represent the basal group of vascular plants and are known to have fungal interactions with arbuscular mycorrhizal fungi, but diversity of endophytic fungi from ferns is rarely studied. Moreover, fungal diversity associated with ferns is likely underestimated as most studies have been performed based on a microscopic or culture-dependent approach. In this study, we investigated the endophytic fungal diversity within roots and sporophore of an endangered Korean fern ( Mankyua chejuense ), and compared it to fungi in surrounding soil using a metabarcoding approach. A high diversity of endophytic fungi (236 OTUs), mostly belonging to Ascomycota, was detected and fungal richness and composition were significantly different between habitats. Indicator species analysis showed that endophytic fungi have similar ecological characteristics to fungal species found from other land plants. Our results suggest that various fungal species are associated with ferns, thus understanding fern-associated fungal diversity can have a great implication for fern biology and conservation. • Endophytic fungal diversity associated with ferns is largely unexplored. • Diversity of fungi associated to fern is explored using a metabarcoding approach. • The endophytic richness and composition are different between habitats. • Many indicator species are similar to the endophytic fungi from other land plants.