In January 2017, Peperomia tetragona was found to be infected with a powdery mildew in Korea. No chasmothecia were observed. The fungus associated with foliar signs of powdery mildew was identified as Podosphaera xanthii using morphological characteristics of the anamorph and molecular analysis of ITS regions. This is the first report of powdery mildew infections on P. tetragona worldwide.