This study aimed to assess the incidence and distribution of toxigenic fungi in Korean oat. Toxigenic fungi were isolated from oat samples collected from 12 oat fields from heading to harvest in 2017 and 2018. A total of 745 fungal colonies were isolated based on morphology and identified using marker genes. About 92% of the fungal isolates were Fusarium spp. and others were Penicillium (5.9%) and Aspergillus (2.1%). Fusarium isolates comprised mostly of F. asiaticum (83.1%), followed by F. incarnatum (5.4%), F. proliferatum (3.5%), F. fujikuroi (2.8%), F. tricinctum species complex (FTSC) 11 (1.5%) and F. graminearum (1.0%). About 97% of F. asiaticum was nivalenol type, and 3-acetyl deoxynivalenol (3.2%) and 15-acetyl deoxynivalenol (0.4%) types also were found. Pathogenicity test of the selected Fusarium isolates revealed that F. asiaticum isolates have a wide range of virulence depending on the tested plants. F. graminearum and FTSC 11 isolates from blighted spikelets were the most virulent in naked oat. All Fusarium isolates (n=18) except one (FTSC 11) produced nivalenol (0.2–7.6 μg/g), deoxynivalenol (0.03–6.1 μg/g), and zearalenone (0.1–27.0 μg/g) on rice medium. This study is first report that F. asiaticum causes Fusarium head blight disease of oat in Korea. These findings demonstrate the dominance of F. asiaticum in oat agroecosystems as in rice, wheat and barley in Korea.