During crop disease surveys in October 2022, we encountered leaf spot symptoms in coastal hogfennel (Peucedanum japonicum) grown in a field in Buyeo, Korea. Disease symptom outbreaks in the field ranged from 5 to 10%. The three fungal isolates obtained from leaf lesions were morphologically identified as Didymella sp. Phylogenetic analyses confirmed a close relationship between the isolates and Didymella acutilobae, and the mycological characteristics were generally consistent with those of D. acutilobae. Pathogenicity of the isolates on leaves of coastal hogfennel was confirmed via artificial inoculation test. To date, this is the first report on the onset of D. acutilobae-induced leaf spot in coastal hogfennel.