Hydrangea petiolaris, belonging to the family Hydrangeaceae, is a vine plant distributed in Ulleung, Jeju, and other southern islands of Korea. In October 2017, a rust fungus was discovered on H. petiolaris in Jeju Island, Korea. To identify the rust fungus, we performed a morphological examination and molecular phylogenetic analysis of the internal transcribed spacer and 28S large subunit rDNA sequences. As a result, the fungus was identified as Pucciniastrum hydrangeae-petiolaris, consistent with previous reports from Japan and Russia, but showed a significant phylogenetic distance from Pucciniastrum hydrangeae reported on Hydrangeae spp. in North America. This is the first record of P. hydrangeae-petiolaris on H. petiolaris in Korea.