Chemotherapy is increasingly used in breast cancer treatment; however, drug resistance remains the major limitation and challenge of present chemotherapy. Previous studies indicated that the combination of nanomaterials and chemotherapy drug could overcome such resistance and exhibit a synergistic anticancer effect. The purpose of this study was to evaluate the antibreast cancer effect of cyclophosphamide, gemcitabine, 5-fluorouracil, oxaliplatin, or doxorubicin combined with silver nanotriangles (AgNTs), and screen out the drug with the most broad-spectrum and strongest synergistic activity. Transmission electron microscopy image showed that the synthesized AgNTs were triangular and truncated triangular in shape with a mean edge length of 126 nm. The synergistic antibreast cancer effect of AgNTs plus cyclophosphamide or gemcitabine was found to be cell type–specific, while 5-fluorouracil, oxaliplatin, and doxorubicin displayed synergistic effects with AgNTs on viabilities of various breast cancer cell lines (MDA-MB-231, MCF-7, and 4T1), and doxorubicin was the strongest in general. Furthermore, the synergism was proved to mainly result from reactive oxygen species–mediated cell apoptosis. These findings could potentially be exploited for new highly efficient combination treatment of breast cancer.