Abstract: The objective of this study is to investigate the sensitivity of Ceratocystis fimbriata to fludioxonil, and evaluate the control efficacy of fludioxonil against the black rot of sweet potatoes during the seedling and storage stages. A total of 64 isolates were collected from sweet potatoes in Henan, Sichuan, Hebei, and Shandong Provinces. With the concave slide tests, the effect of fludioxonil on spore germination and germ tube elongation was observed. The sensitivity of 64 isolates was determined by spore germination and mycelial growth rate methods respectively. Meanwhile, the control efficacies of fludioxonil 50% WP against the black rot of sweet potatoes in the seedling and storage stages were evaluated. The results showed that the conidia germination rate of C. fimbriata decreased gradually and the tortuosity of the germ tube increased gradually with the increase of fludioxonil concentrations. Fludioxonil could also cause premature branching of the germ tube. EC₅₀ values of fludioxonil against spore germination ranged from 0.20 μg/mL to 0.99 μg/mL, with a mean of 0.52 μg/mL. EC₅₀ values of fludioxonil against mycelial growth ranged from 0.17 μg/mL to 0.31 μg/mL, with a mean of 0.24 μg/mL. As the sensitivity frequency showed normal distribution, the mean EC₅₀ values could be regarded as the baseline sensitivity of C. fimbriata to fludioxonil. The control efficacy of fludioxonil 50% WP on seedlings of sweet potato dipped in the suspension of 500 mg a.i./L fludioxonil was 90.24%, which was significantly higher than that of thiophanate-methyl 500 g/L SC at the same concentration during the seedling stage. The control efficacies of fludioxonil dipped in the suspension of fludioxonil at 500 mg a.i./L for two consecutive years were 84.41% and 82.30%, respectively, which were also significantly higher than that of thiophanate-methyl dripped in the suspension of thiophanate-methyl with the same concentration during storage process. The residues of fludioxonil were lower than the maximum residue limit (MRL) at 60 d and 90 d after application. This study suggested fludioxonil has great potential to control the black rot of sweet potatoes during both growth and storage stages.