We presented a case of hepatitis B virus (HBV)-related type III cryoglobulinemia vasculitis (CryoVas) characterized by extremity gangrene in a patient with diabetes. The 60-year-old female had a 10-year history of poorly controlled type 2 diabetes mellitus. She complained of sudden onset pain and swelling of toes which quickly progressed to gangrene, with fingers becoming pain and dark violet. The patient was initially misdiagnosed as diabetic foot (DF). Although DF is one of the common chronic complications of diabetes, it rarely involves the hand. What is more, the ischemic manifestations of the extremity were not consistent with the results of the vascular examination and immune system changes. The patient had Raynaud's phenomenon, arthralgia, and extremity gangrene. Test results showed cryoglobulinemia multiple positive, polyclonal immunoglobulin with rheumatoid factor negative, lower complement 3, leukocytoclastic vasculitis, and HBV infection. HBV-related type III CryoVas was finally diagnosed, and a conservative therapy strategy was given. Six months after treatment with cyclophosphamide, corticosteroid, nucleoside/nucleotide analog therapy, local debridement, and dressing change, she recovered and kept no recurrence by following up for 30 months. To our knowledge, this is the first report of extremity gangrene caused by HBV-related CryoVas in a diabetic patient.