Lenvatinib is a molecular-targeted agent with proven efficacy against hepatocellular carcinoma (HCC). We herein report a case of lenvatinib-associated Fournier gangrene. A 66-year-old man with advanced HCC presented with a high fever 4 weeks after switching to lenvatinib. He had severe erythema in the inguinal region, and abdominal computed tomography revealed extensive emphysema and scrotal abscesses. He was diagnosed with Fournier's gangrene, and his symptoms were successfully treated with local debridement and antimicrobial therapy. Although reports of lenvatinib-associated Fournier's gangrene are rare, they should be kept in mind, as the condition could progress rapidly and have poor outcomes.