To observe the clinical efficacy and adverse reactions of skin cancer treated with heavy ion beams(,12,C,6+,), 12 patients (volunteers) accepted the clinical therapy. The heavy ion beam energy was 100 MeV/u, RBE (Relative biologic effectiveness) value was 2.5—3.0, and radiation absorbed dose was 60—70 GyE for 6—7 d with 2.5—5.41 Gy/d. Clinical efficacy was valuated by tumor fashion in 3 months after treatment and acute adverse reactions judged by radiation therapy oncology group based on criteria of acute radiation injury. 12 patients were followed up for 3 months and detected. Among them 10 patients were completely remitted (CR) and 2 partly remitted (PR). No adverse reaction appeared except that grade 1—2 skin side-effect was observed. It is suggested that heavy ion beams are effective and safe treatment rays to skin cancer. It can shorten treatment time markedly and has no serious adverse reactions.