Aspergillus flavus contamination is common in various food and feed ingredients, and it poses to serious threats to human and animal health. Curcumin is a plant-derived polyphenol that exhibits antifungal activity. In this study, the antifungal effect of curcumin on A. flavus was evaluated, and the underlying mechanism was investigated. Curcumin effectively decreased aflatoxin B1 synthesis and suppressed A. flavus infection in peanut. Curcumin inhibited the mycelial growth and sporulation of A. flavus. Ergosterol biosynthesis in A. flavus was suppressed, and cell membrane permeability was enhanced. The pathogenicity of A. flavus was also reduced by curcumin treatment. Curcumin induced ROS burst in the hyphae of A. flavus, and those damages could be reversed by exogenous superoxide dismutase, suggesting that curcumin inhibited A. flavus possibly via inducing oxidative stress. These results indicate that curcumin has the potential to be used as a preservative to control A. flavus contamination in food and feedstuff.