Oat is a minor forage crop grown in Taiwan. Only a few historical records of oat rust disease have been reported in the country. Therefore, the pathogen population remains poorly characterized. A rust-like disease outbreak was detected at the Experimental Farm of National Taiwan University in 2019, which caused significant damage to field experiments. To determine the identity of the pathogen responsible for this disease outbreak, we collected infected foliar material. Disease signs suggested infection by the oat crown rust fungus. Hence, common procedures in rust pathology were applied to confirm the identity of the pathogen with phenotypic and molecular diagnostic techniques. A total of 50 field pathogen samples from infected oat cultivars were collected in 2019, and 5 single-pustule rust isolates were obtained in 2020 and 2021. These isolates were initially identified as