Provided is to enhance the therapeutic effect of an iontophoretic preparation for treatment of breast cancer or mastitis.An iontophoretic preparation for treatment of breast cancer and/or mastitis containing, as an active ingredient, a nonsteroidal anti-inflammatory analgesic agent and/or an anticancer agent, wherein an electrolyte is topically administered through the nipple part into the mammary gland; subsequently, a donor is applied to the nipple part; and the active ingredient is topically administered through the nipple part into the mammary gland by application of current.