Taiwan acacia (Acacia confusa Merr.) is a native tree, is widely distributed at low and midelevations in Taiwan, and is commonly used for afforestation. A symptom of vascular wilt of Taiwan acacia was observed in Lioukuei District, Kaohsiung City in 2018. Seedlings initially appeared dehydrated, and gradually the entire seedling became wilted, eventually resulting in death. Black-brown necrosis occurred on the main roots and the cut ends of basal stems. The pathogen was isolated and purified from necrotic tissues. A fungus could be obtained from all affected seedlings. Judging from morphological features, this fungus is Fusarium oxysporum. Sequencing of the nuclear ribosomal DNA intergenic spacer (IGS) region of this fungus was performed, which suggested that this fungus is F. oxysporum f. sp. koae. This is the first report of this fungus in Taiwan. This fungus accounted for a 60%~70% mortality of seedlings at a Taiwan acacia nursery in Lioukuei. It is apparently an important disease in Taiwan acacia nurseries.