Abstract: Acral malignant melanoma, as the main type of melanoma in China, is commonly seen in plantar lesions. Due to similar clinical manifestation, it is easy to be misdiagnosed as diabetic foot ulcers. We report a case of diabetes mellitus complicated with malignant melanoma, which was misdiagnosed as diabetic ulcer in the right foot, thus delaying treatment. Therefore, when diabetic foot lesions are characterized by atypical ulcers and the foot ulcers remain unhealed, pathological examination should be performed to exclude the possibility of malignant melanoma.