This invention discloses uses for estrone in preparing anti-ovarian cancer and/or breast cancer products. This invention provides uses for estrone in the preparation of products to treat ovarian cancer and/or breast cancer. From carrying out cancer drug repositioning for the FDA- and CFDA-approved drug estrone, experiments for this invention show, based on screening of non-anti-cancer drugs for various cancer cell lines (tissue types) and mutation sites, that estrone has a new use as an anti-ovarian cancer and/or anti-breast cancer medication, thus achieving a new purpose for an old drug.