Abstract: To valorize agricultural waste, sweet potato leaves were subjected to the solid-state fermentation using Eurotium cristatum. The dynamic changes in phenolic compounds, enzymatic activity, and antioxidant capacity during fermentation were studied. Results indicated that the total phenolic and flavonoid contents increased significantly in the initial stage of fermentation, reaching peak values of 12.31 mg/g and 11.1 mg/g on the 6^th d, respectively, which were 1.97 and 2.31 times higher than that of potato leaves in the unfermented group. Enzymatic activities of α-amylase (R²=0.749), β-glucosidase (R²=0.844), cellulase (R²=0.674), protease (R²=0.772), and polyphenol oxidase (R²=0.822) showed a positive correlation with the total phenolic content (P<0.05). HPLC analysis revealed that the phenolic profile of fermented sweet potato leaves was similar to that of unfermented leaves. Except catechin, contents of each phenolic compound was significantly increased after fermentation. Furthermore, in the DPPH and ABTS⁺ assays, a significant improvement (P<0.05) was observed in the free radical scavenging ability of the methanolic extracts of fermented leaves. The fermented sample on the 6^th d has the greatest radical scavenging activity against ABTS⁺, which is 2.46 times that of the unfermented sample, and DPPH, which is 2.19 times that of the unfermented sample. Principal component analysis indicated that the increase in the phenolic content was the result of synergistic action of hydrolytic enzymes secreted by E. cristatum. The improvement in the antioxidant capacity in response to the E. cristatum fermentation was mainly attributed to the release of gallic acid, quercetin, and p-coumaric acid during fermentation. These findings suggest that solid-state fermentation with E. cristatum is an effective way to improve the phenolic content and antioxidant capacity of sweet potato leaves while the optimum period of fermentation was 6 d.