New species of arbuscular mycorrhizal fungi (Glomeromycota), Acaulospora jejuensis, was isolated from rhizosphere soils of Miscanthus sinensis in the grassland in Jeju Island of Korea. The species was identified using the morphological characteristics of the spores and the molecular phylogenetic analysis using partial DNA sequences from small subunit rDNA (SSU), internal transcribed spacer (ITS), and large subunit rDNA (LSU). Phylogenetic analysis placed the fungal species in a distinct clade within genus Acaulospora. Also, the species exhibited the morphological characteristics distinct from the other members of the genus. Therefore, Acaulospora jejuensis was described as a novel species from Korea.