This study aims to determine the effects of the natural product aloesin against . The results exposed that aloesin had a high inhibitory effect on appressorium formation (the EC value was 175.26 μg/mL). Microscopic examination revealed that 92.30 ± 4.26% of spores could be broken down by 625.00 μg/mL of aloesin, and the formation rate of appressoria was 4.74 ± 1.00% after 12 h. mycelial growth was weaker than that on the control. The enzyme activity analysis results indicated that aloesin inhibited the activities of polyketolase (PKS), laccase (LAC), and chain-shortening catalytic enzyme (Aayg1), which are key enzymes in melanin synthesis. The inhibition rate by aloesin of PKS, LAC, and Aayg1 activity was 32.51%, 33.04%, and 43.38%, respectively. The proteomic analysis showed that actin expression was downregulated at 175.62 μg/mL of aloesin, which could reduce actin bundle formation and prevent the polar growth of hyphae in . This is the first report showing that aloesin effectively inhibits conidia morphology and appressorium formation in .