A 37-year-old Japanese woman received an anticancer drug for 5 years following resection of mammary cancer and then developed widespread mollusca contagiosa, which we considered to be caused by immunosuppression induced by the chemotherapy. Because OK-432 (penicillin-treated and heat-treated lyophilized powder by a substrain of Streptococcus pyogenes A) was expected to be effective for immunosuppression, we tried its topical injection. The skin lesions disappeared almost completely within three months. OK-432 therapy is considered hopeful for treating viral skin diseases, even in immunosuppressed patients.