We experienced 3 cases of anti-cancer drug-resistant recurrent breast cancer with liver metastasis showing significant improvement by S-1. Almost all patients maintained the full dose through the whole course of treatment, and the drug showed good tolerability. Furthermore, long-term therapeutic efficacy(more than 2 years)and QOL have been maintained for all patients. We concluded that S-1 is not only effective as a therapeutic agent, but is safe and maintains QOL.