Kaposi's sarcoma (KS) is known as multiple idiopathic hemorrhagic sarcoma. Its pathogenesis is complicated and related to abnormal angiogenesis, virus infections, etc. Human Herpes Virus-8 (HHV8) is increasingly linked to AIDS-associated KS. Herein, we reported a case of an 80-year-old male of Han ethnicity who developed dark red nodules on the inner popliteal fossa of his left leg without obvious predisposing causes two years ago. The nodules gradually increased in number, with unequal sizes, accompanied by discomfort. The patient was admitted to our hospital. Using clinical and tissue pathology combined with immunohistochemistry, the patient was diagnosed as the classical Kaposi's sarcoma of Han ethnicity. Local radiotherapy with electron beam ( total dose 5000 cgy, 6 million electron volts, 5 mm depth, 200 cgy each time, 25 times in total) was adopted for treatment. After 10 days of radiotherapy, the nodules diminished and partially degraded, while after one month of radiotherapy, most nodules gradually vanished.