Matricaria chamomilla L. (Asteraceae), known as German chamomile, is popular in Korea for medicinal and ornamental purposes. During September and October 2019, powdery mildew symptoms on the leaves and stems of M. chamomilla were observed on 50% of 300 plants surveyed at an herb garden in Namyangju (37°35′29"N 127°13′52"E), Korea. Conidiophores were cylindrical, 110–190 × 10–12 μm and produced conidia in chains. Conidia were ellipsoid-ovoid to doliiform, 28–40 × 18–23 μm, and contained conspicuous fibrosin bodies. Dark brown chasmothecia were gregarious, partly embedded in the hyphal mat, spherical, and 85–100 µm in diameter. Appendages were hyphoid, 1–4-septate, and brown but paler upwards. Each chasmothecium contained a single ascus. Asci were sessile, 8-spored, and 54–70 × 48–56 μm. Ascospores were oval to subglobose, and 14–18 × 12–15 µm. These characteristics were consistent with those of Podosphaera xanthii (Castagne) U. Braun & Shishkoff (Braun and Cook 2012). To confirm the morphological identification, rDNA was extracted from the reference isolate KUS-F31455 deposited at Korea University Herbarium. PCR products were amplified using the primers ITS1F and PM6 for the internal transcribed spacer (ITS) region, and PM3 and TW14 for the large subunit (LSU) region of the rDNA. The sequences were deposited in GenBank (Accession Nos. OK161015 for ITS, OK161017 for LSU). A Blastn search using ITS and LSU sequences showed 99.33 to 100% similarity with P. xanthii (e.g., MF663781, MG657015 for ITS; MT826247, MT919354 for LSU). Several species of Podosphaera on Matricaria spp. have been recorded from Europe, North America, Egypt, and Japan (Farr and Rossman 2021). Recently, ITS sequence of a powdery mildew on M. chamomilla in Iran (MF663781) clustered with P. xanthii (Khodaparast 2016). To our knowledge, this is the first report of powdery mildew disease associated with P. xanthii on M. chamomilla in Korea.