Erysiphe zelkovae is one of the main pathogens causing significant damage to Zelkova serrata in East Asia. Despite the global diversity of Zelkova spp., E. zelkovae has been reported only on Z. serrata from East Asian countries (Japan, China, and Korea). Mycological information regarding this fungus is insufficient in terms of sequenced nucleotides and detailed morphological characteristics. This study presents a detailed characterization of the holomorph of E. zelkovae and its taxonomic placement through molecular phylogenetic analyses using the internal transcribed spacer region and large subunit gene sequences from three representative Korean specimens. This study confirmed the identity of E. zelkovae as a distinct species among the Erysiphe section Uncinula species on host plants belonging to the family Ulmaceae.