The patient is a 56-year-old Japanese woman who suffered from breast cancer and ovarian cancer at intervals of 6 years, and was also complicated by two episodes of dermatomyositis, each of which occurred simultaneously with each of two cancers. When she was 51 years old, she developed dermatomyositis for the first time 6 months after the resection of breast cancer, whose histological type was tubular adenocarcinoma. The dermatomyositis remitted without oral corticosteroids in 2 months, and the remission had continued for 6 years. However, at the age of 56, dermatomyositis abruptly recurred with a pruritic generalized rash, Gottron's papules and elevated serum CK levels. Examination for malignancy revealed an ovarian tumor, which was diagnosed as serous papillaly adenocarcinoma, and the surgery was performed. After the resection of the ovarian cancer, skin rash was improved dramatically and CK levels were normalized again without oral corticosteroids. Since there were no evidences of recurrence of the breast cancer, it was considered that each episode of dermatomyositis was associated with each of the cancers, respectively. We report this rare and interesting case to consider the etiology of cancer-associated myositis as a paraneoplastic syndrome, since the two cancers have different histological types.